Monoamine compound, charge transport material, composition for charge transport film, organic electroluminescent element, organic el display, and organic el lighting

ABSTRACT

A monoamine compound characterized by being represented by the following general formula (1). 
     
       
         
         
             
             
         
       
     
     [In general formula (1), R 1  to R 3  each independently represent a phenyl group which may have a substituent in at least one of o- and m-positions, in which the substituent may be bonded to each other to form a cyclic structure. R 1  to R 3  are a group different from each other.]

TECHNICAL FIELD

The present invention relates to a monoamine compound which is thermallyand electrochemically stable and is soluble in various solvents, acharge transport material including the monoamine compound, acomposition for charge transport film which contains the chargetransport material, an organic electroluminescent element which includesa layer containing the charge transport material and has highluminescent efficiency and high driving stability, and an organic ELdisplay and an organic EL lighting each equipped with the element.

BACKGROUND ART

In recent years, electroluminescent elements employing an organic thinfilm (organic electroluminescent elements) are being developed. Examplesof methods for forming an organic thin film include a vacuum depositionmethod and a wet film formation method. Of these, the wet film formationmethod has advantages, for example, that no vacuum process is necessaryand film formation in a larger area is easy, and that it is easy toincorporate a mixture of a plurality of materials having variousfunctions into one layer (coating fluid).

Mainly used as the materials of luminescent layers formed by a wet filmformation method are high-molecular materials such aspoly(p-phenylenevinylene) derivatives and polyfluorene derivatives.However, high-molecular materials have problems including the following:(1) it is difficult to regulate the degree of polymerization andmolecular weight distribution of the high-molecular materials, (2)deterioration due to residual end groups occurs during continuousdrivings, and (3) it is difficult to highly purify the materialsthemselves and the materials contain impurities.

Due to those problems, the organic electroluminescent elements producedby a wet film formation method have poorer driving stability thanorganic electroluminescent elements produced by a vacuum depositionmethod, and have not reached a practical level at present, except someelements.

In patent document 1 is described an organic electroluminescent elementemploying an organic thin film formed by a wet film formation methodfrom not a high-molecular compound but a mixture of a plurality oflow-molecular materials (charge transport materials or luminescentmaterials) in an attempt to overcome those problems. As charge transportmaterials having the property of transporting holes, compounds H-1 andH-2 shown below are used therein.

Meanwhile, with respect to organic electroluminescent elements employingan organic thin film which contains a plurality of low-molecularmaterials and has been formed by a wet film formation method, non-patentdocument 1 and patent document 2 describe an organic electroluminescentelement which utilizes phosphorescence so as to have enhancedluminescent efficiency. Compounds H-3, H-4, and H-5 shown below are usedas charge transport materials therein.

CONVENTIONAL-ART DOCUMENTS Patent Documents

-   Patent Document 1: JP-A-11-273859-   Patent Document 2: JP-A-2007-110093

Non-Patent Document

-   Non-Patent Document 1: Japanese Journal of Applied Physics, Vol. 44,    No. 1B, pp. 626-629, 2005

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

However, the compounds H-1, H-2, H-3, H-4, and H-5 do not always havesufficient solubility in solvents. Although it is therefore necessary touse a halogenated solvent, e.g., chloroform, as a coating-fluid solvent,such halogenated solvents impose a heavy environmental burden.Furthermore, there is a possibility that impurities contained in thehalogenated solvent might deteriorate the materials. It is thought thatorganic electroluminescent elements produced by a wet film formationmethod using a halogenated solvent do not have sufficient drivingstability.

In addition, the compounds H-1, H-2, H-3, and H-4 have a low glasstransition temperature and, hence, it is thought that the organicelectroluminescent elements disclosed in patent document 1 andnon-patent document 1 have room for improvement in heat resistance.Moreover, the compounds H-1, H-2, H-3, H-4, and H-5 are exceedingly aptto crystallize, and it is not easy to obtain an even amorphous filmtherefrom by a wet film formation method.

Furthermore, in the case where a phosphorescent material is used as aluminescent material, an organic electroluminescent element formed usinga composition containing the compound H-1 and the phosphorescentmaterial is thought to have low luminescent efficiency because thecompound H-1 has a low triplet excitation level.

Consequently, the invention has been achieved in view of the state ofthe conventional-art techniques, and a subject for the invention is toprovide a charge transport material which is thermally andelectrochemically stable and is soluble in solvents and a compositionfor charge transport film which contains the charge transport material.

Another object of the invention is to provide an organicelectroluminescent element having high luminescent efficiency and highdriving stability and an organic EL display and an organic EL lightingwhich each are equipped with the element.

Means for Solving the Problems

The present inventors diligently made investigations. As a result, theinventors have found that a monoamine compound represented by thefollowing general formula (1) has excellent solubility in solvents, ishighly noncrystalline, can hence be formed into a thin film by a wetfilm formation method, and further has excellent charge-transportingproperties, excellent durability concerning electricaloxidation/reduction, and a high triplet excitation level, and that useof the monoamine compound in an organic electroluminescent element canhence impart high luminescent efficiency and high driving stabilitythereto. The invention has been thus completed.

Namely, essential points of the invention reside in the following 1 to11.

1. A monoamine compound characterized by being represented by thefollowing general formula (1).

[In general formula (1), R¹ to R³ each independently represent a phenylgroup which may have a substituent in at least one of o- andm-positions, in which the substituent may be bonded to each other toform a cyclic structure, and R¹ to R³ is a group different from eachother.]2. The monoamine compound according to 1 above, which further comprisesa partial structure represented by the following structural formula(2-1).

[In structural formula (2-1), the phenyl group may further have asubstituent, in which the substituent may have been bonded to each otherto form a cyclic structure.]3. The monoamine compound according to 1 or 2 above, wherein in thegeneral formula (1), R¹ to R³ each independently are a phenyl groupwhich may have a substituent in an m-position.4. The monoamine compound according to any one of 1 to 3 above, whereinin the general formula (1), at least one of R¹ to R³ is a groupincluding a partial structure represented by the following generalformula (2-2).

[X in general formula (2-2) represents any one of —NR⁴— (where R⁴represents an aryl group which may have a substituent), —O—, and —S—.The X-containing fused ring in general formula (2-2) may further have asubstituent, in which the substituent may have been bonded to each otherto form a cyclic structure.]5. The monoamine compound according to 4 above, wherein the partialstructure represented by general formula (2-2) is a partial structurerepresented by the following structural formula (3).

[In structural formula (3), the N-carbazole ring may further have asubstituent, and the substituent may have been bonded to each other toform a cyclic structure.]6. The monoamine compound according to any one of 1 to 5 above, whereinin the general formula (1), at least one of R¹ to R³ is a grouprepresented by the following general formula (11).

[In general formula (11), Q represents a direct bond or any linkinggroup. Y has the same meaning as the X contained in the general formula(2-2). The Y-containing fused ring in general formula (11) may have asubstituent, and the substituent may be bonded to each other to form acyclic structure.]7. The monoamine compound according to any one of 1 to 6 above, whichhas a solubility in m-xylene of 5% by mass or more at 25° C. andatmospheric pressure.8. A charge transport material comprising the monoamine compoundaccording to any one of 1 to 7 above.9. A composition for charge transport film, which comprises the chargetransport material according to 8 above and a solvent.10. An organic electroluminescent element which comprises a substrateand, disposed thereover, an anode, a cathode, and a luminescent layerinterposed between the electrodes, wherein the luminescent layercontains the charge transport material according to 8 above.11. An organic EL display comprising the organic electroluminescentelement according to 10 above.12. An organic EL lighting comprising the organic electroluminescentelement according to 10 above.

Effects of the Invention

According to the monoamine compound of the invention, the chargetransport material including the monoamine compound, and the compositionfor charge transport film which contains the charge transport material,it is possible to easily form, by a wet film formation method, anorganic thin film containing a material which is thermally andelectrochemically stable and has a high triplet excitation level, andthis facilitates production of an organic electroluminescent elementhaving a larger area.

Furthermore, the organic electroluminescent element obtained using thecharge transport material of the invention and using the composition forcharge transport film which contains the charge transport material canbe made to luminesce at a high luminance and high efficiency and hasimproved stability, in particular, improved driving stability.

Since the charge transport material of the invention has excellentfilm-forming properties, charge-transporting properties, luminescentcharacteristics, and heat resistance, the charge transport material canbe applied to not only film formation by a vacuum deposition method butalso film formation by a wet film formation method.

Moreover, since the charge transport material of the invention and thecomposition for charge transport film which contains the chargetransport material have excellent film-forming properties,charge-transporting properties, luminescent characteristics, and heatresistance, the material and the composition can be applied to theformation of organic layers such as a hole injection layer, holetransport layer, luminescent layer, electron injection layer, andelectron transport layer according to the layer configuration of theelement.

Consequently, the organic electroluminescent element obtained using thecharge transport material of the invention and using the composition forcharge transport film which contains the charge transport material isthought to be applied to flat panel displays (e.g., displays for OAcomputers and wall-mounted TV receivers), vehicle-mounted displayelements, cell phone displays, light sources taking advantage of thefeature of a surface light emitter (e.g., the light source of a copierand the backlights of a liquid-crystal display and instrument), displaypanels, and marker lights, and have a high technical value.

Furthermore, the charge transport material of the invention and thecomposition for charge transport film which contains the chargetransport material can be effectively utilized not only in organicelectroluminescent elements but also in electrophotographicphotoreceptors and the like because the material and the compositionessentially have excellent stability to oxidation and reduction.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a sectional view diagrammatically illustrating an example ofthe structure of an organic electroluminescent element of the invention.

MODES FOR CARRYING OUT THE INVENTION

Modes for carrying out the invention will be explained below in detail.However, the following explanations on constituent elements are forembodiments (representative embodiments) of the invention, and theinvention should not be construed as being limited to the embodimentsunless the invention departs from the spirit thereof.

<Monoamine Compound>

The monoamine compound of the invention (hereinafter referred to also as“compound (1)”) is characterized by being represented by the followinggeneral formula (1).

In general formula (1), R¹ to R³ each independently represent a phenylgroup which may have a substituent in at least one of o- andm-positions, and the substituents may be bonded to each other to form acyclic structure. R¹ to R³ are groups different from each other.

[1. Structural Features]

Since compound (1) has a triphenylamine structure, this compound has theexcellent ability to transport charges (holes) and has a high tripletexcitation level and high heat resistance.

R¹ to R³ in compound (1), i.e., the three substituents possessed by thetriphenylamine structure, differ from each other, and compound (1) hencehas no axis of symmetry. Consequently, compound (1) is exceedinglyhighly noncrystalline, has excellent solubility in various organicsolvents, and can form an organic thin film which is amorphous and doesnot crystallize readily.

Furthermore, since R¹ to R³ each independently are a phenyl group whichmay have a substituent in at least one of o- and m-positions(hereinafter, such structure is sometimes referred to as“non-p-position-substituted partial structure”), compound (I) hasfurther improved noncrystalline properties and better solubility.

In addition, the non-p-position-substituted partial structure has suchproperties that R¹ to R³ are less apt to receive an electron as comparedwith phenyl groups having a substituent in the p-position. It is thoughtthat compound (1), which contains the partial structure, is hence lessapt to be decomposed (namely, the compound is electrochemically stable)and this leads to prevention of a decrease in the working life oforganic electroluminescent elements.

From the standpoint of further improving the solubility, it is preferredthat R¹ to R³ should each independently be a phenyl group which may havea substituent in an m-position.

[2. Range of Molecular Weight]

The molecular weight of compound (1) is generally preferably 5,000 orlower, more preferably 4,000 or lower, even more preferably 3,000 orlower, and is generally preferably 200 or higher, more preferably 300 orhigher, even more preferably 400 or higher.

Compound (1) having a molecular weight within that range is easy topurify and has satisfactory heat resistance because the glass transitiontemperature, melting point, vaporization temperature, and the like ofthe compound are high.

[3. Properties] (1) Glass Transition Temperature

It is preferred that compound (1) should have a glass transitiontemperature of generally 50° C. or higher. From the standpoint of heatresistance, the glass transition temperature thereof is preferably 80°C. or higher, more preferably 110° C. or higher.

(2) Vaporization Temperature

It is preferred that compound (1) should have a vaporization temperatureof generally 300° C. to 800° C. It is preferred that the chargetransport material of the invention should have no crystallizationtemperature between the glass transition temperature and thevaporization temperature.

(3) Solubility

It is preferred that compound (1) should be a compound which candissolve in m-xylene in an amount of 5% by mass or more under theconditions of 25° C. and atmospheric pressure, from the standpoints ofensuring solubility in solvents and obtaining the property of formingfilms in a wet film formation method. The solubility thereof ispreferably 10% by mass or more, more preferably 15% by mass or more.Although there is no particular upper limit on the solubility thereof,the solubility is generally preferably 50% by mass or less.

[4] Axis of Symmetry

In case where two or more of the substituents of a triphenylamine arethe same, this compound has an axis of symmetry in the molecule like thecompounds represented by the following general formulae (I-1) to (I-3).

In general formulae (I-1) to (I-3), R¹¹, R¹², R²¹, R³¹, R³², and R³³each independently represent a phenyl group which may have asubstituent, and the substituents may have been bonded to each other toform a ring.

In contrast, all of R¹ to R³ in compound (1) differ from each other and,hence, compound (1) has no axis of symmetry in the molecule.Consequently, the charge transport material of the invention is highlynoncrystalline and has enhanced solubility in solvents.

[5. R¹ to R³]

In formula (1), R¹ to R³ each independently represent a phenyl groupwhich may have a substituent in at least one of o- and m-positions, andthe substituents may have been bonded to each other to form a cyclicstructure. However, none of R¹, R², and R³ is a group which is the sameas any of the others.

Examples of the substituents possessed by the phenyl groups representedby R¹ to R³ include alkyl groups which may have a substituent, alkenylgroups which may have a substituent, alkynyl groups which may have asubstituent, aralkyl groups which may have a substituent, an amino groupwhich may have a substituent, arylamino groups having an aromatichydrocarbon group which has 6-12 carbon atoms and may have asubstituent, heteroarylamino groups having a 5- or 6-membered aromaticheterocycle which may have a substituent, acylamino groups having anacyl group which has 2-10 carbon atoms and may have a substituent,alkoxy groups which may have a substituent, aryloxy groups which mayhave a substituent, heteroaryloxy groups which may have a substituent,acyl groups which may have a substituent, alkoxycarbonyl groups whichmay have a substituent, aryloxycarbonyl groups which may have asubstituent, alkylcarbonyloxy groups which may have a substituent,halogen atoms, carboxy, cyano, hydroxy, mercapto, alkylthio groups whichmay have a substituent, arylthio groups which may have a substituent,sulfonyl groups which may have a substituent, silyl group which may havea substituent, boryl group which may have a substituent, phosphino groupwhich may have a substituent, aromatic hydrocarbon groups which may havea substituent, and aromatic heterocyclic groups which may have asubstituent.

The alkyl groups which may have a substituent preferably are linear orbranched alkyl groups having 1-8 carbon atoms. Examples thereof includemethyl, ethyl, n-propyl, 2-propyl, n-butyl, isobutyl, and tert-butyl.

The alkenyl groups which may have a substituent preferably are alkenylgroups having 2-9 carbon atoms. Examples thereof include vinyl, allyl,and 1-butenyl.

The alkynyl groups which may have a substituent preferably are alkynylgroups having 2-9 carbon atoms. Examples thereof include ethynyl andpropargyl.

The aralkyl groups which may have a substituent preferably are aralkylgroups having 7-15 carbon atoms. Examples thereof include benzyl.

The amino group which may have a substituent preferably is an alkylaminogroup having one or more alkyl groups which each have 1-8 carbon atomsand may have a substituent. Examples thereof include methylamino,dimethylamino, diethylamino, and dibenzylamino.

Examples of the arylamino groups having an aromatic hydrocarbon groupwhich has 6-12 carbon atoms and may have a substituent includephenylamino, diphenylamino, and ditolylamino.

Examples of the heteroarylamino groups having a 5- or 6-memberedaromatic heterocycle which may have a substituent include pyridylamino,thienylamino, and dithienylamino.

Examples of the acylamino groups having an acyl group which has 2-10carbon atoms and may have a substituent include acetylamino andbenzoylamino.

The alkoxy groups which may have a substituent preferably are alkoxygroups which have 1-8 carbon atoms and may have a substituent. Examplesthereof include methoxy, ethoxy, and butoxy.

The aryloxy groups which may have a substituent preferably are aryloxygroups which have an aromatic hydrocarbon group having 6-12 carbonatoms. Examples thereof include phenyloxy, 1-naphthyloxy, and2-naphthyloxy.

The heteroaryloxy groups which may have a substituent preferably areheteroaryloxy groups having a 5- or 6-membered aromatic heterocyclicgroup. Examples thereof include pyridyloxy and thienyloxy.

The acyl groups which may have a substituent preferably are acyl groupswhich have 2-10 carbon atoms and may have a substituent. Examplesthereof include formyl, acetyl, and benzoyl.

The alkoxycarbonyl groups which may have a substituent preferably arealkoxycarbonyl groups which have 2-10 carbon atoms and may have asubstituent. Examples thereof include methoxycarbonyl andethoxycarbonyl.

The aryloxycarbonyl groups which may have a substituent preferably arearyloxycarbonyl groups which have 7-13 carbon atoms and may have asubstituent. Examples thereof include phenoxycarbonyl.

The alkylcarbonyloxy groups which may have a substituent preferably arealkylcarbonyloxy groups which have 2-10 carbon atoms and may have asubstituent. Examples thereof include acetoxy.

The halogen atoms preferably are a fluorine atom and a chlorine atom.

The alkylthio groups which may have a substituent (preferably alkylthiogroups having 1-8 carbon atoms; examples thereof include methylthio andethylthio.),

The arylthio groups which may have a substituent preferably are arylthiogroups having 6-12 carbon atoms. Examples thereof include phenylthio and1-naphthylthio.

Examples of the sulfonyl groups which may have a substituent includemesyl and tosyl.

Examples of the silyl group which may have a substituent includetrimethylsilyl and triphenylsilyl.

Examples of the boryl group which may have a substituent includedimesitylboryl.

Examples of the phosphino group which may have a substituent includediphenylphosphino.

Examples of the aromatic hydrocarbon groups which may have a substituentinclude monovalent groups derived from 5- or 6-membered monocycles ordi- to pentacyclic fused rings, such as a benzene ring, naphthalenering, anthracene ring, phenanthrene ring, perylene ring, tetracene ring,pyrene ring, benzpyrene ring, chrysene ring, triphenylene ring, andfluoranthene ring.

Examples of the aromatic heterocyclic groups which may have asubstituent include monovalent groups derived from 5- or 6-memberedmonocycles or di- to tetracyclic fused rings, such as a furan ring,benzofuran ring, thiophene ring, benzothiophene ring, pyrrole ring,pyrazole ring, imidazole ring, oxadiazole ring, indole ring, carbazolering, pyrroloimidazole ring, pyrrolopyrazole ring, pyrrolopyrrole ring,thienopyrrole ring, thienothiophene ring, furopyrrole ring, furofuranring, thienofuran ring, benzisoxazole ring, benzisothiazole ring,benzimidazole ring, pyridine ring, pyrazine ring, pyridazine ring,pyrimidine ring, triazine ring, quinoline ring, isoquinoline ring,cinnoline ring, quinoxaline ring, benzimidazole ring, perimidine ring,and quinazoline ring.

In the case where those substituents further have substituents, examplesof the substituents include the substituents shown above as examples.

From the standpoints of improving electrochemical durability andimproving heat resistance, the substituents of the phenyl groupsrepresented by R¹ to R³ are as follows. Preferred examples thereof arearomatic hydrocarbon groups which may have a substituent and aromaticheterocyclic groups which may have a substituent, and more preferredexamples thereof are a phenyl group which may have a substituent andmonovalent groups derived from the 5- or 6-membered monocycles or di- totetracyclic fused rings. Even more preferred examples thereof are aphenyl group which is unsubstituted or has one or two substituents andan unsubstituted carbazole ring or benzofuran ring. The substituents ofR¹ to R³ may have two or more of the substituents shown above asexamples, and may have been bonded to each other.

From the standpoint of further improving solubility and noncrystallineproperties, it is preferred that the substituents of the phenyl groupsrepresented by R′ to R³ should be alkyl groups which may have asubstituent. More preferred are methyl, ethyl, n-propyl, 2-propyl,n-butyl, isobutyl, and tert-butyl. Even more preferred are methyl andethyl.

The phenyl groups represented by R¹ to R³ differ in the substituentintroduced to the benzene ring of the phenyl group or differ withrespect to the presence or absence of a substituent. R¹ to R³ hencediffer from each other.

R¹ to R³ are phenyl groups which differ from each other as describedabove. It is preferred that the difference in the number of carbon atomsbetween the group among R¹ to R³ which has a largest total number ofcarbon atoms, including the carbon atoms of the substituent, and thegroup which has a smallest total number of carbon atoms (hereinafterreferred to as “carbon number difference in R¹-R³”) should be 10 ormore.

It is preferred that the difference in the number of carbon atomsbetween the group among R¹ to R³ which has a largest total number ofcarbon atoms, including the carbon atoms of the substituent, and thegroup which has a second largest total number of carbon atoms should be5 or more. It is preferred that the difference in the number of carbonatoms between the group among R¹ to R³ which has a smallest total numberof carbon atoms, including the carbon atoms of the substituent, and thegroup which has a second largest total number of carbon atoms should be5 or more.

Furthermore, it is more preferred that the difference in the number ofcarbon atoms between the group having a largest total number of carbonatoms and the group having a second largest total number of carbon atomsand the difference in the number of carbon atoms between the lattergroup and the group having a smallest total number of carbon atoms eachshould be 5 or more.

Compound (1) in which the carbon number difference in R¹-R³ is 10 ormore and each difference in the number of carbon atoms between two of R¹to R³ is 5 or more has even higher noncrystalline properties and evenbetter solubility in various organic solvents. This compound (1) canform an organic thin film which is highly noncrystalline and does notcrystallize readily.

The upper limit of the carbon number difference in R¹-R³ is preferably300, more preferably 150. By regulating the carbon number difference inR¹-R³ to a value not larger than the upper limit, thecharge-transporting ability can be prevented from decreasing.

Furthermore, the upper limit of each difference in the number of carbonatoms between two of R¹ to R³ is preferably 200, more preferably 100. Byregulating each difference in the number of carbon atoms between two ofR¹ to R³ to a value not larger than the upper limit, thecharge-transporting ability can be prevented from decreasing.

Incidentally, the upper limit of the total number of carbon atoms ineach of R¹ to R³ is preferably 350, more preferably 150.

[6] Especially Preferred Partial Structures

In the case where the monoamine compound of the invention is to be usedas the charge transport material which will be described later, it isespecially preferred that compound (1) should have an m-phenylene group,which is represented by the following structural formula (2-1), in themolecule, from the standpoint of further improving solubility insolvents. It is preferred that the m-phenylene group should be containedas a partial structure of any one of R¹ to R³.

In structural formula (2-1), the phenyl group may further have one ormore substituents, and the substituents may have been bonded to eachother to form a cyclic structure.

In the case where the monoamine compound of the invention is to be usedas a charge transport material, it is especially preferred that compound(1) should have in the molecule a group including a partial structurerepresented by the following general formula (2-2), from the standpointof improving heat resistance while maintaining a high triplet excitationlevel.

In the case where the charge transport material of the inventioncontains a group including a partial structure represented by thefollowing general formula (2-2), it is preferred that at least one of R¹to R³ in compound (1) should be a group including the partial structurerepresented by the following general formula (2-2).

X in general formula (2-2) represents any one of —NR⁴— (where R⁴represents an aryl group which may have a substituent), —O—, and —S—.The X-containing fused ring in general formula (2-2) may further haveone or more substituents, and the substituents may have been bonded toeach other to form a cyclic structure.

From the standpoints of heat resistance and solubility, it is preferredthat X in general formula (2-2) should be —NR⁴— (where R⁴ represents anaryl group which may have a substituent) or —O—.

The X-containing fused ring in general formula (2-2) may further haveone or more substituents. Examples of the substituents include the samegroups as the substituents which may be possessed by the above-describedphenyl groups represented by R¹ to R³ contained in compound (1). In theinvention, it is preferred that the X-containing fused ring in generalformula (2-2) should have no substituent.

From the standpoint of enabling the charge transport material of theinvention to more effectively exhibit excellent electron-transportingability, which is a feature of the material, it is preferred that anyone of R¹ to R³ in compound (1) should contain a group including apartial structure represented by general formula (2-2) as stated above.

It is preferred that the partial structure represented by generalformula (2-2) should be an N-carbazolyl group, which is represented bythe following structural formula (3), from the standpoints ofcharge-transporting properties and heat resistance.

In structural formula (3), the N-carbazole ring may further have one ormore substituents, and the substituents may have been bonded to eachother to form a cyclic structure.

From the standpoint of further improving solubility in solvents, it isespecially preferred that at least one of R¹ to R³ in compound (1)should be a group represented by the following general formula (11).

In general formula (11), Q represents a direct bond or any linkinggroup. Y has the same meaning as the X contained in general formula(2-2). The Y-containing fused ring in general formula (11) may have oneor more substituents, and the substituents may be bonded to each otherto form a cyclic structure.

The Y-containing fused ring in general formula (11) may further have asubstituent, and examples of the substituent include the same groups asthe substituents which may be possessed by the above-described phenylgroups represented by R¹ to R³. In the invention, it is preferred thatthe Y-containing fused ring in general formula (11) should have nosubstituent.

Q is a direct bond or any linking group. In the case where Q is anylinking group, this group preferably is a divalent aromatic hydrocarbongroup. Specifically, the linking group preferably is a phenylene groupor is two or more phenylene groups linked to each other.

Examples of the two or more phenylene groups linked to each otherinclude a biphenylene group and a terphenylene group.

It is most preferred that Q should be directly bonded to a meta-positionatom of the benzene ring bonded to the main framework of the compoundrepresented by general formula (1), as shown in general formula (11).

Namely, it is most preferred that the part (Y-containing fused ring)which mainly serves to transport holes should be bonded through abenzene ring in a meta position. As a result, not only compound (1) hasimproved solubility in solvents, but also the excellent electrochemicalstability, excellent heat resistance, and high triplet excitation levelare not impaired because of the excellent heat resistance, excellentelectrochemical stability, and high triplet excitation level of thebenzene ring. Consequently, it is preferred that Q should be a groupcomposed of m-phenylene groups linked to each other. The number of suchm-phenylene groups linked to each other is preferably 1-5, morepreferably 2-3.

It is especially preferred that compound (1) in the invention should bea compound which is represented by the following general formula (4) andhas no axis of symmetry (hereinafter often referred to as “compound(4)”).

In general formula (4), R¹ and R² have the same meanings as the R¹ andR² contained in general formula (1). Q and Y have the same meanings asin general formula (11).

R¹ and R² in general formula (4) have the same meanings as the R¹ and R²contained in general formula (1), and preferred examples thereof are asexplained above in the section [5. R¹ to R³].

It is especially preferred that the partial structure in general formula(4) which corresponds to the R³ contained in general formula (1) shouldbe a group represented by the following general formula (6) or (7), fromthe standpoint of improving solubility in solvents and heat resistance.

In general formula (6), Z represents a phenylene group which may have asubstituent; at least the first phenylene group, among the x phenylenegroups, that is bonded to the main framework of the compound representedby general formula (1) is an m-phenylene group; and x represents aninteger of 2-6.

In general formula (6), x is 2-6 and is preferably 2-4, especiallypreferably 2-3.

In general formula (7), Z represents a phenylene group which may have asubstituent; at least the first phenylene group, among the x phenylenegroups, that is bonded to the main framework of the compound representedby general formula (1) is an m-phenylene group; and x represents aninteger of 2-6.

In general formula (7), x is 2-4 and is preferably 2-3.

On the other hand, it is especially preferred that R¹ in general formula(4) should be a group represented by the following general formula (8)or (9).

In general formulae (8) and (9), Z represents a phenylene group whichmay have a substituent; at least the first phenylene group, among thex-1 phenylene groups, that is bonded to the main framework of thecompound represented by general formula (1) is an m-phenylene group; andx represents an integer of 2-6.)

Furthermore, it is especially preferably that R² should be a grouprepresented by the following general formula (10).

—(Z)_(y)-Ph  (10)

In general formula (10), Z represents a phenylene group which may have asubstituent; at least the first phenylene group, among the y phenylenegroups, that is bonded to the main framework of the compound representedby general formula (1) is an m-phenylene group; Ph represents a phenylgroup which may have a substituent; and y represents an integer of 1-5.

Here, y is 1-5, and is preferably 1-3.

[8. Exemplification]

Preferred examples of the monoamine compound of the invention are shownbelow. However, the invention should not be construed as being limitedto the following examples.

[9. Synthesis Methods]

The charge transport material of the invention can be synthesized, forexample, from an arylamine compound as a starting material bysuccessively introducing aromatic rings.

(C—N Coupling Reaction)

The substrate is reacted with a halide or trifluoromethanesulfonic acidester reagent which has an aromatic hydrocarbon group, in the presenceof a base using a transition metal element catalyst. Thus, an aminogroup can be introduced to the aromatic hydrocarbon group.

Isolation and purification can be conducted by means of a combination ofoperations, such as, e.g., distillation, filtration, extraction,recrystallization, reprecipitation, suspension washing, andchromatography.

Examples of the transition metal element catalyst include palladiumcatalysts and copper catalysts. Palladium catalysts are preferred fromthe standpoints of ease of the reaction and high yield.

The base is not particularly limited. For example, use can be made ofpotassium carbonate, cesium carbonate, tert-butoxysodium, triethylamine,and the like.

With respect to a solvent, toluene is preferred when a palladiumcatalyst is used. When a copper catalyst is used, pyridine,N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and the like arepreferred.

Compound (1) according to the invention can be synthesized also from atrihalide of a triarylamine as a starting material by successivelyconducting coupling reactions.

(C—C Coupling Reaction)

The substrate is reacted with an organometallic reagent having anaromatic hydrocarbon group in a nonpolar or polar solvent in thepresence of a base using a transition metal element catalyst. Thus, thearomatic hydrocarbon group can be introduced to the substrate.

Isolation and purification can be conducted by means of a combination ofoperations, such as, e.g., distillation, filtration, extraction,recrystallization, reprecipitation, suspension washing, andchromatography.

Examples of the organometallic reagent include organoboron reagents,organomagnesium reagents, and organozinc reagents. Of these, organoboronreagents are preferred from the standpoint of ease of handling.

Examples of the transition metal element catalyst includeorganopalladium catalysts, organonickel catalysts, organocoppercatalysts, organoplatinum catalysts, organorhodium catalysts,organoruthenium catalysts, and organoiridium catalysts. Of these,organopalladium catalysts are preferred from the standpoints of ease ofthe reaction and high yield.

The base is not particularly limited. However, metal hydroxides, metalsalts, organic alkali metal reagents, and the like are preferred.

The solvent to be used is not particularly limited so long as thesolvent does not act on the substrate. Examples thereof includealiphatic hydrocarbons such as hexane, heptane, and cyclohexane;aromatic hydrocarbons such as benzene, toluene, and xylene; ethers suchas dimethoxyethane, tetrahydrofuran, and dioxane; alcohols such asethanol and propanol; and water. These solvents can be used alone or asa mixture thereof.

According to need, a surfactant can be added in an amount of 1-100 mol%.

[Charge Transport Material]

The charge transport material of the invention includes a monoaminecompound represented by general formula (1). Since the monoaminecompound has excellent solubility in solvents and high noncrystallineproperties, a thin film can be formed by a wet film formation method.

Furthermore, since the monoamine compound included in the chargetransport material of the invention further has excellentcharge-transporting properties and excellent durability concerningelectrical oxidation/reduction and has a high triplet excitation level,use of the charge transport material in organic electroluminescentelements renders a high luminescent efficiency and high drivingstability possible.

[Composition for Charge Transport Film]

The composition for charge transport film of the invention contains thecharge transport material of the invention described above, and it ispreferred that the composition should be used for organicelectroluminescent elements.

[1] Solvent

It is preferred that the composition for charge transport film of theinvention, in particular, the composition for charge transport film tobe used as a composition for organic electroluminescent elements, shouldcontain a solvent.

The solvent to be contained in the composition for charge transport filmof the invention is not particularly limited so long as the solutesincluding the charge transport material of the invention satisfactorilydissolve therein.

Since the charge transport material of the invention has exceedinglyhigh solubility in solvents, various solvents can be applied. Forexample, use can be made of aromatic hydrocarbons such as toluene,xylene, mesitylene, cyclohexylbenzene, and tetralin; halogenatedaromatic hydrocarbons such as chlorobenzene, dichlorobenzene, andtrichlorobenzene; aromatic ethers such as 1,2-dimethoxybenzene,1,3-dimethoxybenzene, anisole, phenetole, 2-methoxytoluene,3-methoxytoluene, 4-methoxytoluene, 2,3-dimethylanisole, and2,4-dimethylanisole; aromatic esters such as phenyl acetate, phenylpropionate, methyl benzoate, ethyl benzoate, propyl benzoate, andn-butyl benzoate; alicyclic ketones such as cyclohexanone andcyclooctanone; aliphatic ketones such as methyl ethyl ketone and dibutylketone; alicyclic alcohols such as methyl ethyl ketone, cyclohexanol,and cyclooctanol; aliphatic alcohols such as butanol and hexanol;aliphatic ethers such as ethylene glycol dimethyl ether, ethylene glycoldiethyl ether, and propylene glycol 1-monomethyl ether acetate (PGMEA);aliphatic esters such as ethyl acetate, n-butyl acetate, ethyl lactate,and n-butyl lactate; and the like.

Of these, aromatic hydrocarbons such as toluene, xylene, mesitylene,cyclohexylbenzene, and tetralin are preferred from the standpoints oflow solubility of water therein and little tendency to alter.

Organic electroluminescent elements employ a large number of materialswhich deteriorate considerably by the action of moisture, e.g., thecathode. There is hence a possibility that when moisture is present inthe composition, the film formed through drying might contain moistureremaining therein and the residual moisture might reduce thecharacteristics of the element. It is therefore preferred to reduce thewater content of the composition.

Examples of methods for reducing the water content of the compositioninclude sealing with nitrogen gas, use of a drying agent, solventdehydration conducted beforehand, and use of a solvent in which water ispoorly soluble. Use of a solvent in which water is poorly soluble ispreferred of these methods because the phenomenon in which during a wetfilm formation step, the coating film of the solution absorbsatmospheric moisture to blush can be prevented in this case.

From such a standpoint, the solvent to be contained in the compositionfor charge transport film of the invention should have a watersolubility therein at 25° C. of preferably 1% by mass or less, morepreferably 0.1% by mass or less. It is also preferred that this solventshould be contained in the composition in an amount of 10% by mass ormore.

From the standpoint of inhibiting film formation stability from beingreduced by solvent vaporization from the composition during wet filmformation, the boiling point of the solvent of the composition forcharge transport film is preferably 100° C. or higher, more preferably150° C. or higher, even more preferably 200° C. or higher.

For obtaining a more even film, it is necessary that the solvent shouldvaporize at an appropriate rate from the liquid film immediately afterformation of the film. In order for the solvent to satisfy this, thelower limit of the boiling point of the solvent is generally preferably80° C., more preferably 100° C., even more preferably 120° C. The upperlimit thereof is generally preferably lower than 270° C., morepreferably lower than 250° C., even more preferably lower than 230° C.

A solvent which satisfies those requirements, i.e., the requirementsconcerning solubility of solutes therein, vaporization rate, and watersolubility therein, may be used alone. However, in the case where it isimpossible to select a solvent which satisfy all the requirements, amixture of two or more solvents can be used.

[2] Luminescent Material

It is preferred that the composition for charge transport film of theinvention, in particular, the composition for charge transport filmwhich is to be used as a composition for organic electroluminescentelements, should contain a luminescent material.

The term luminescent material means an ingredient which mainlyluminesces in the composition of charge transport layer formation of theinvention, and the luminescent material corresponds to a dopantingredient in organic electroluminescent devices. Namely, when generally10-100%, preferably 20-100%, more preferably 50-100%, and mostpreferably 80-100% of the quantity of light (unit: cd/m²) emitted from acomposition for charge transport film is ascertained to be attributableto luminescence from a certain ingredient material, then the ingredientis defined as a luminescent material.

As the luminescent material, any desired known material can be used. Forexample, one of fluorescent materials or one of phosphorescent materialscan be used alone, or a mixture of two or more of these materials can beused. From the standpoint of inner-quantum efficiency, phosphorescentmaterials are preferred.

It is preferred that the luminescent material should have a maximumluminescence peak wavelength in the range of 390-490 nm.

It is possible to reduce the symmetry or stiffness of the molecule of aluminescent material or to introduce an oleophilic substituent such asan alkyl group thereto, for the purpose of improving solubility insolvents.

Examples of fluorescent dyes which give blue luminescence includeperylene, pyrene, anthracene, coumarin, p-bis(2-phenylethenyl)benzene,and derivatives of these.

Examples of green fluorescent dyes include quinacridone derivatives andcoumarin derivatives.

Examples of yellow fluorescent dyes include rubrene and perimidonederivatives.

Examples of red fluorescent dyes include DCM type compounds, benzopyranderivatives, Rhodamine derivatives, benzothioxanthene derivatives, andazabenzothioxanthene.

Examples of phosphorescent materials include organometallic complexescontaining a metal selected from Groups 7 to 11 of the periodic table.

Preferred examples of the metal in the phosphorescent organometalliccomplexes containing a metal selected from Groups 7 to 11 of theperiodic table include ruthenium, rhodium, palladium, silver, rhenium,osmium, iridium, platinum, and gold. Preferred as these organometalliccomplexes are compounds represented by the following general formula (V)and formula (VI).

mL_((q-j))L′_(j)  (V)

In general formula (V), M represents a metal and q represents thevalence of the metal. L and L′ represent a bidentate ligand. Symbol jrepresents an integer of 0-2.

In general formula (VI), M^(d) represents a metal, and T represents acarbon atom or a nitrogen atom. R⁹² to R⁹⁵ each independently representa substituent. However, when T is a nitrogen atom, R⁹⁴ and R⁹⁵ areabsent.

The compounds represented by general formula (V) are explained firstbelow.

In general formula (V), M represents any metal. Preferred examplesthereof include the metals enumerated above as metals selected fromGroups 7 to 11 of the periodic table.

The bidentate ligands L and L′ in general formula (V) each represent aligand including the following partial structure.

The following are especially preferred as L′ from the standpoint of thestability of the complex.

In the partial structures of L and L′, ring A1 represents an aromatichydrocarbon group or an aromatic heterocyclic group, and ring A2represents a nitrogen-containing aromatic heterocyclic group. Thesegroups may have substituents.

In the case where rings A1 and A2 have substituents, suitable examplesof the substituents include halogen atoms such as a fluorine atom; alkylgroups such as methyl and ethyl; alkenyl groups such as vinyl;alkoxycarbonyl groups such as methoxycarbonyl and ethoxycarbonyl; alkoxygroups such as methoxy and ethoxy; aryloxy groups such as phenoxy andbenzyloxy; dialkylamino groups such as dimethylamino and diethylamino;diarylamino groups such as diphenylamino; carbazolyl; acyl groups suchas acetyl; haloalkyl groups such as trifluoromethyl; cyano; and aromatichydrocarbon groups such as phenyl, naphthyl, and phenanthyl.

Suitable examples of the compounds represented by general formula (V)include compounds represented by the following formulae (Va), (Vb), and(Vc).

In general formula (Va), M^(a) represents a metal, and w represents thevalence of the metal. Ring A1 represents an aromatic hydrocarbon groupwhich may have a substituent, and ring A2 represents anitrogen-containing aromatic heterocyclic group which may have asubstituent.

In general formula (Vb), M^(b) represents a metal, and w represents thevalence of the metal. Ring A1 represents an aromatic hydrocarbon groupwhich may have a substituent or an aromatic heterocyclic group which mayhave a substituent, and ring A2 represents a nitrogen-containingaromatic heterocyclic group which may have a substituent.

In general formula (Vc), M^(c) represents a metal, and w represents thevalence of the metal. Symbol j represents an integer of 0-2. Ring A1 andring A1′ each independently represent an aromatic hydrocarbon groupwhich may have a substituent or an aromatic heterocyclic group which mayhave a substituent. Furthermore, ring A2 and ring A2′ each independentlyrepresent a nitrogen-containing aromatic heterocyclic group which mayhave a substituent.

Suitable examples of the groups constituting ring A1 and ring A1′ ingeneral formulae (Va), (Vb), and (Vc) include phenyl, biphenyl,naphthyl, anthryl, thienyl, furyl, benzothienyl, benzofuryl, pyridyl,quinolyl, isoquinolyl, and carbazolyl.

Suitable examples of the groups constituting ring A2 and ring A2′include pyridyl, pyrimidyl, pyrazyl, triazyl, benzothiazole group,benzoxazole group, benzimidazole group, quinolyl, isoquinolyl,quinoxalyl, and phenanthridyl.

Furthermore, examples of the substituents which may be possessed by ringA1, ring A1′, ring A2, and ring A2′ include halogen atoms such as afluorine atom; alkyl groups such as methyl and ethyl; alkenyl groupssuch as vinyl; alkoxycarbonyl groups such as methoxycarbonyl andethoxycarbonyl; alkoxy groups such as methoxy and ethoxy; aryloxy groupssuch as phenoxy and benzyloxy; dialkylamino groups such as dimethylaminoand diethylamino; diarylamino groups such as diphenylamino; carbazolyl;acyl groups such as acetyl; haloalkyl groups such as trifluoromethyl;and cyano.

In the case where the substituents are alkyl groups, it is preferredthat the groups each should have generally 1-6 carbon atoms.

In the case where the substituents are alkenyl groups, it is preferredthat the groups each should have generally 2-6 carbon atoms.

In the case where the substituents are alkoxycarbonyl groups, it ispreferred that the groups each should have generally 2-6 carbon atoms.

In the case where the substituents are alkoxy groups, it is preferredthat the groups each should have generally 1-6 carbon atoms.

In the case where the substituents are aryloxy groups, it is preferredthat the groups each should have generally 6-14 carbon atoms.

In the case where the substituents are dialkylamino groups, it ispreferred that the groups each should have generally 2-24 carbon atoms.

In the case where the substituents are diarylamino groups, it ispreferred that the groups each should have generally 12-28 carbon atoms.

In the case where the substituents are acyl groups, it is preferred thatthe groups each should have generally 1-14 carbon atoms.

In the case where the substituents are haloalkyl groups, it is preferredthat the groups each should have generally 1-12 carbon atoms.

Those substituents may be bonded to each other to form a ring. Forexample, the substituent possessed by ring A1 and the substituentpossessed by ring A2 may be bonded to each other to form a fused ring,or the substituent possessed by ring A1′ and the substituent possessedby ring A2′ may be bonded to each other to form a fused ring. Examplesof such fused rings include a 7,8-benzoquinoline group.

Preferred of those substituents of ring A1, ring A1′, ring A2, and ringA2′ are alkyl groups, alkoxy groups, aromatic hydrocarbon groups, cyano,halogen atoms, haloalkyl groups, diarylamino groups, and carbazolyl.

Examples of M^(a), M^(b), and M^(c) include the same metals as themetals enumerated above with regard to M. Preferred of these areruthenium, rhodium, palladium, silver, rhenium, osmium, iridium,platinum, and gold.

Specific examples of the organometallic complexes represented by generalformula (V), (Va), (Vb), or (Vc) are shown below. However, the complexesshould not be construed as being limited to the following compounds(wherein Ph′ represents phenyl).

Especially preferred of the organometallic complexes represented bygeneral formulae (V), (Va), (Vb), and (Vc) are: complexes having a2-arylpyridine type ligand, i.e., 2-arylpyridine, as at least one of theligands L and L′; such complexes in which one or more substituents havebeen bonded to the 2-arylpyridine; and such complexes in which thesubstituents have been bonded to each other to form a fused ring.

Furthermore, the compounds described in International Publication No.2005/019373 are also usable.

Next, the compounds represented by general formula (VI) are explained.

M^(d) in general formula (VI) represents a metal, and examples thereofinclude the metals enumerated above as metals selected from Groups 7 to11 of the periodic table. Of these, suitable examples include ruthenium,rhodium, palladium, silver, rhenium, osmium, iridium, platinum, andgold. Preferred are divalent metals such as platinum and palladium.

In general formula (VI), R⁹² and R⁹³ each independently represent ahydrogen atom, halogen atom, alkyl, aralkyl, alkenyl, cyano, amino,acyl, alkoxycarbonyl, carboxyl, alkoxy, alkylamino, aralkylamino,haloalkyl, hydroxy, aryloxy, aromatic hydrocarbon group, or aromaticheterocyclic group.

In the case where T is a carbon atom, R⁹⁴ and R⁹⁵ each independentlyrepresent a substituent examples of which are the same as in the case ofR⁹² and R⁹³. As stated above, R⁹⁴ and R⁹⁵ are absent when T is anitrogen atom.

R⁹² to R⁹⁵ may further have a substituent. The substituent in this caseis not particularly limited, and the substituent can be any desiredgroup.

Furthermore, R⁹² to R⁹⁵ may be bonded to each other to form a ring, andthis ring may further have any desired substituent.

Specific examples (T-1 and T-10 to T-15) of the organometallic complexesrepresented by general formula (VI) are shown below. However, thecomplexes should not be construed as being limited to the followingexample compounds, wherein Me represents methyl and Et represents ethyl.

[3] Other Ingredients

The composition for charge transport film of the invention, inparticular, the composition for charge transport film which is to beused as a composition for organic electroluminescent elements, maycontain other various solvents according to need besides the solvent andluminescent material described above. Examples of the other solventsinclude amides, such as N,N-dimethylformamide and N,N-dimethylacetamide,and dimethyl sulfoxide. The composition may further contain variousadditives including a leveling agent and an antifoamer.

Furthermore, in order to prevent two or more layers from beingcompatible with each other when these layers are superposed by a wetfilm formation method, a photocurable resin or a thermosetting resin maybe incorporated beforehand for the purpose of curing and insolubilizingany of the layers after formation thereof.

[4] Concentration of Materials in the Composition for Charge TransportFilm and Incorporation Ratio Thereof.

In the composition for charge transport film, in particular, in thecomposition for organic electroluminescent elements, the concentrationof solids such as the charge transport material, the luminescentmaterial, and the ingredients which can be added according to need(e.g., a leveling agent) is as follows. The lower limit of theconcentration thereof is generally preferably 0.01% by mass, morepreferably 0.05% by mass, even more preferably 0.1% by mass, especiallypreferably 0.5% by mass, most preferably 1% by mass.

The upper limit thereof is generally preferably 80% by mass, morepreferably 50% by mass, even more preferably 40% by mass, especiallypreferably 30% by mass, most preferably 20% by mass.

Regulating the concentration thereof to a value not lower than the lowerlimit makes it easy to form a thick film in thin-film formation. On theother hand, regulating the concentration thereof to a value not higherthan the upper limit makes it easy to form a thin film.

In the composition for charge transport film of the invention, inparticular, in the composition for organic electroluminescent elements,the content ratio by mass of the luminescent material to the chargetransport material is as follows. The lower limit of the content ratiois generally preferably 0.1/99.9, more preferably 0.5/99.5, even morepreferably 1/99, most preferably 2/98.

The upper limit thereof is generally preferably 50/50, more preferably40/60, even more preferably 30/70, most preferably 20/80.

By regulating the mass ratio thereof to a value within that range, asufficient luminescent efficiency can be obtained.

[5] Method for Preparing the Composition for Charge Transport Film

The composition for charge transport film of the invention, inparticular, the composition for organic electroluminescent elements, canbe prepared by dissolving solutes including the charge transportmaterial, the luminescent material, and various additives which can beadded according to need, such as a leveling agent and an antifoamer, ina suitable solvent.

It is usually preferred to dissolve the solutes while stirring thesolution, in order to reduce the time period required for thedissolution step and to keep the concentration of the solutes in thecomposition constant. The dissolution step may be conducted at ordinarytemperature. However, when the rate of dissolution is low, the solutescan be dissolved while heating the mixture. After completion of thedissolution step, a filtration step such as filtering may be conductedaccording to need.

[6] Properties, Etc. Of the Composition for Charge Transport Film

(Water Concentration)

In the case where an organic electroluminescent element is producedthrough film formation by a wet film formation method using thecomposition for charge transport film of the invention (composition fororganic electroluminescent elements), the presence of moisture in thecomposition for organic electroluminescent elements to be used resultsin the formation of a film which contains moisture and has impairedevenness. It is therefore preferred that the water content of thecomposition for charge transport film of the invention, in particular,the composition for organic electroluminescent elements, should be aslow as possible.

In general, organic electroluminescent elements employ a large number ofmaterials which deteriorate considerably by the action of moisture,e.g., the cathode. There is hence a possibility that when moisture ispresent in the composition for charge transport film, the film formedthrough drying might contain moisture remaining therein and the residualmoisture might reduce the characteristics of the element. The presenceof moisture in the composition is hence undesirable.

Specifically, the water content of the composition for charge transportfilm of the invention, in particular, the composition for organicelectroluminescent elements, is generally preferably 1% by mass orlower, more preferably 0.1% by mass or lower, even more preferably 0.01%by mass or lower.

With respect to methods for determining the water concentration in thecomposition for charge transport film, the method described in JapaneseIndustrial Standards under “Method of Determining Moisture Content ofChemical Product” (JIS K0068: 2001) is preferred. For example, thecomposition can be analyzed by the Karl Fischer's reagent method (JISK0211-1348) or the like.

(Evenness)

It is preferred that the composition for charge transport film of theinvention, in particular, the composition for organic electroluminescentelements, should be in the state of a liquid which is even at ordinarytemperature, from the standpoint of enhancing stability in a wet filmformation process, e.g., stability in ejection from nozzles in filmformation by ink-jet printing.

The term “state of a liquid which is even at ordinary temperature” meansthat the composition is a liquid constituted of an even phase and thiscomposition contains no particulate ingredient having a particlediameter of 0.1 μm or more.

(Properties)

The viscosity at 25° C. of the composition for charge transport film ofthe invention, in particular, the composition for organicelectroluminescent elements, is as follows. The lower limit thereof isgenerally preferably 2 mPa·s, more preferably 3 mPa·s, even morepreferably 5 mPa·s. The upper limit thereof is generally preferably1,000 mPa·s, more preferably 100 mPa·s, even more preferably 50 mPa·s.

The composition having a viscosity regulated so as to be not lower thanthe lower limit is less apt to arouse troubles such as, for example,excessive flow of the liquid film in a film formation step and theresultant unevenness of the coating surface and nozzle ejection failuresin film formation by ink-jet printing. Furthermore, the composition forcharge transport film, in particular, the composition for organicelectroluminescent elements, that has a viscosity regulated so as to benot higher than the upper limit is less apt to cause nozzle clogging infilm formation by ink-jet printing.

The surface tension at 20° C. of the composition for charge transportfilm of the invention, in particular, the composition for organicelectroluminescent elements, is generally preferably less than 50 mN/m,more preferably less than 40 mN/m.

By regulating the surface tension thereof so as to be lower than theupper limit, the composition can be prevented from posing, for example,a problem that the liquid for film formation has reducedsubstrate-wetting properties, i.e., the liquid film has impairedleveling properties, and this is apt to result in a disordered filmsurface through drying.

The vapor pressure at 25° C. of the composition for charge transportfilm of the invention, in particular, the composition for organicelectroluminescent elements, is generally preferably 50 mmHg or less,more preferably 10 mmHg or less, even more preferably 1 mmHg or less.

By regulating the vapor pressure thereof so as to be not higher than theupper limit, problems such as a change in solute concentration due tosolvent vaporization can be prevented.

<Configuration of the Organic Electroluminescent Element>

The organic electroluminescent element of the invention is notparticularly limited so long as the element includes a substrate and,formed thereover, a pair of electrodes and one or more organic layers,at least one of which contains the charge transport material of theinvention.

The organic layers vary depending on the layer configuration of theorganic electroluminescent element. However, examples thereof include ahole injection layer, a hole transport layer, a luminescent layer, ahole blocking layer, an electron transport layer, and an electroninjection layer.

In the case where the organic electroluminescent element of theinvention includes one organic layer, this means that the organic layeris a luminescent layer, and this luminescent layer hascharge-transporting ability and contains the charge transport materialof the invention.

On the other hand, in the case of an organic electroluminescent elementincluding a plurality of organic layers, this element may be one inwhich at least one of the hole injection layer, hole transport layer,luminescent layer, hole blocking layer, electron transport layer, andelectron injection layer contains the charge transport material of theinvention.

The layer configuration of the organic layers in the organicelectroluminescent element having a plurality of organic layers is notparticularly limited so long as the element can luminesce. However,examples of the element include organic electroluminescent elementshaving the following layer configurations.

1) An organic electroluminescent element configured at least of aluminescent layer and an electron transport layer.2) An organic electroluminescent element configured at least of a holetransport layer and a luminescent layer.3) An organic electroluminescent element configured at least of a holetransport layer, a luminescent layer, and an electron transport layer.

A layer configuration of the organic electroluminescent element of theinvention and general methods for forming the layers, etc. are explainedbelow by reference to FIG. 1. Incidentally, for reasons of theconvenience of illustration, the dimensional proportions in the drawingare not always the same as in the dimensional proportions explainedbelow.

FIG. 1 is a diagrammatic sectional view illustrating one example of theorganic electroluminescent element according to the invention. Theorganic electroluminescent element shown in FIG. 1 has a structureincluding a substrate 1 and, successively formed thereon, an anode 2, ahole injection layer 3, a hole transport layer 4, a luminescent layer 5,a hole blocking layer 6, an electron transport layer 7, an electroninjection layer 8, and a cathode 9.

The term “wet film formation method” in the invention means a method inwhich a film is formed by a wet process or the like, such as, forexample, spin coating, dip coating, die coating, bar coating, bladecoating, roll coating, spray coating, capillary coating, ink-jetprinting, screen printing, gravure printing, or flexographic printing.

Preferred of these film formation methods are spin coating, spraycoating, and ink-jet printing. This is because these techniques suitwith the liquid nature of the coating composition to be used forproducing the organic electroluminescent element.

(Substrate)

The substrate 1 serves as the support of the organic electroluminescentelement, and use may be made of a plate of quartz or glass, a metalplate, a metal foil, a plastic film or sheet, or the like.

Especially preferred are a glass plate and plates of transparentsynthetic resins such as a polyester, polymethacrylate, polycarbonate,polysulfone, and the like.

In the case of using a synthetic-resin substrate, it is necessary totake account of gas barrier properties. In case where the substrate hastoo low gas barrier properties, there are cases where the surroundingair might pass through the substrate to deteriorate the organicelectroluminescent element.

Consequently, one of preferred methods is to form a dense silicon oxidefilm or the like on at least one surface of a synthetic-resin substrateto ensure gas barrier properties.

(Anode)

The anode 2 serves to inject holes into layers located on theluminescent layer side. The anode 2 is usually constituted of a metal,e.g., aluminum, gold, silver, nickel, palladium, platinum, etc., a metaloxide, e.g., an indium and/or tin oxide, a metal halide, e.g., copperiodide, carbon black, a conductive polymer, e.g.,poly(3-methylthiophene), polypyrrole, or polyaniline, or the like.

Usually, the anode 2 is frequently formed by sputtering, vacuumdeposition, or the like. In the case where an anode 2 is to be formedusing fine particles of a metal, e.g., silver, fine particles of copperiodide or the like, carbon black, fine particles of a conductive metaloxide, fine particles of a conductive polymer, or the like, use may bemade of a method in which such fine particles are dispersed in anappropriate binder resin solution and the dispersion is applied to asubstrate 1 to form an anode 2.

Furthermore, in the case of a conductive polymer, an anode 2 can beformed by directly forming a thin film on a substrate 1 throughelectrolytic polymerization or by applying the conductive polymer to asubstrate 1 (Appl. Phys. Lett., Vol. 60, p. 2711, 1992).

The anode 2 usually has a single-layer structure. However, the anode 2can have a multilayer structure composed of a plurality of materials,according to need.

The thickness of the anode 2 varies depending on the degree oftransparency required. When transparency is required, it is preferredthat the anode 2 should be regulated so as to have a visible-lighttransmittance of generally preferably 60% or higher, more preferably 80%or higher. In this case, the thickness of the anode 2 is generallypreferably 5 nm or more, more preferably 10 nm or more, and is generallypreferably 1,000 nm or less, more preferably 500 nm or less.

When the anode 2 may be opaque, this anode 2 can have any desiredthickness and may be identical with the substrate 1. Furthermore, it ispossible to superpose a different conductive material on the anode 2.

It is preferred that the surface of the anode 2 should be subjected toan ultraviolet (UV)/ozone treatment or a treatment with an oxygen plasmaor argon plasma for the purposes of removing impurities adherent to theanode 2 and regulating ionization potential to improve hole injectionproperties.

(Hole Injection Layer)

The hole injection layer 3 is a layer which transports holes from theanode 2 to the luminescent layer 5, and is usually formed on the anode2.

Methods for forming the hole injection layer 3 according to theinvention are not particularly limited, and either a vacuum depositionmethod or a wet film formation method may be used. However, from thestandpoint of diminishing dark spots, it is preferred to form the holeinjection layer 3 by a wet film formation method.

The thickness of the hole injection layer 3 is generally preferably 5 nmor more, more preferably 10 nm or more, and is generally preferably1,000 nm or less, more preferably 500 nm or less.

<Formation of Hole Injection Layer by Wet Film Formation Method>

In the case where a hole injection layer 3 is to be formed by a wetprocess, materials for constituting the hole injection layer 3 areusually mixed with an appropriate solvent (solvent for hole injectionlayer) to prepare a composition for film formation (composition for holeinjection layer formation).

Subsequently, this composition for hole injection layer formation isapplied by a suitable technique to the layer (usually, the anode) whichis to underlie the hole injection layer 3, and the resultant coatingfilm is dried to thereby form a hole injection layer 3.

(Hole-Transporting Compound)

The composition for hole injection layer formation usually contains ahole-transporting compound, as a material for constituting the holeinjection layer, and a solvent.

The hole-transporting compound may usually be a high-molecular compoundsuch as a polymer or a low-molecular compound such as a monomer so longas the compound has hole-transporting properties and is for use in thehole injection layers of organic electroluminescent elements. It is,however, preferred that the hole-transporting compound should be ahigh-molecular compound.

From the standpoint of a barrier to charge injection from the anode 2into the hole injection layer 3, it is preferred that thehole-transporting compound should be a compound having an ionizationpotential of 4.5 eV to 6.0 eV.

Examples of the hole-transporting compound include aromatic aminederivatives, phthalocyanine derivatives, porphyrin derivatives,oligothiophene derivatives, polythiophene derivatives, benzylphenylderivatives, a compound including tertiary amines linked with a fluorenegroup, hydrazone derivatives, silazane derivatives, silanaminederivatives, phosphamine derivatives, quinacridone derivatives,polyaniline derivatives, polypyrrole derivatives, polyphenylenevinylenederivatives, polythienylenevinylene derivatives, polyquinolinederivatives, polyquinoxaline derivatives, and carbon.

Incidentally, the term “derivative” in the invention has the followingmeaning. In the case of an aromatic amine derivative, for example, thatterm includes the aromatic amine itself and compounds having thearomatic amine as the main framework, and these compounds may bepolymers or monomers.

Any one of such hole-transporting compounds may be contained alone as amaterial for the hole injection layer 3, or two or more thereof may becontained as the material.

In the case where two or more hole-transporting compounds are contained,any desired combination of such compounds may be used. However, it ispreferred to use one or more aromatic tertiary amine high-molecularcompounds in combination with one or more other hole-transportingcompounds.

Of the compounds shown above as examples, aromatic amine compounds arepreferred from the standpoints of noncrystallinity and visible-lighttransmittance. In particular, aromatic tertiary amine compounds arepreferred. The term aromatic tertiary amine compound means a compoundhaving an aromatic tertiary amine structure, and includes a compoundhaving a group derived from an aromatic tertiary amine.

The kind of aromatic tertiary amine compound is not particularlylimited. However, a high-molecular compound (polymeric compound made upof consecutive repeating units) having a weight-average molecular weightof 1,000-1,000,000 is more preferred from the standpoint of evenluminescence based on the effect of surface smoothing.

Preferred examples of the aromatic tertiary amine high-molecularcompound include high-molecular compounds having a repeating unitrepresented by the following formula (VII).

In general formula (VII), Ar¹ and Ar² each independently represent anaromatic hydrocarbon group which may have a substituent or an aromaticheterocyclic group which may have a substituent. Ar³ to Ar⁵ eachindependently represent an aromatic hydrocarbon group which may have asubstituent or an aromatic heterocyclic group which may have asubstituent. Y represents a linking group selected from the followinglinking groups. Of Ar¹ to Ar⁵, two groups bonded to the same nitrogenatom may be bonded to each other to form a ring.

In the general formulae, Ar⁶ to Ar¹⁶ each independently represent anaromatic hydrocarbon group which may have a substituent or an aromaticheterocyclic group which may have a substituent. R¹⁰¹ and R¹⁰² eachindependently represent a hydrogen atom or any desired substituent.

The aromatic hydrocarbon groups and aromatic heterocyclic groupsrepresented by Ar¹ to Ar¹⁶ preferably are groups derived from any of abenzene ring, naphthalene ring, phenanthrene ring, thiophene ring, andpyridine ring, from the standpoints of the solubility, heat resistance,and suitability for hole injection and transport of the high-molecularcompound. More preferred are groups derived from a benzene ring and anaphthalene ring.

The aromatic hydrocarbon groups and aromatic heterocyclic groupsrepresented by Ar¹ to Ar¹⁶ may have further substituents. The molecularweights of the substituents are generally preferably 400 or lower, morepreferably 250 or lower.

Preferred examples of the substituents are alkyl groups, alkenyl groups,alkoxy groups, aromatic hydrocarbon groups, aromatic heterocyclicgroups, and the like.

In the case where R¹⁰¹ and R¹⁰² are any desired substituents, examplesof the substituents include alkyl groups, alkenyl groups, alkoxy groups,silyl group, siloxy group, aromatic hydrocarbon groups, and aromaticheterocyclic groups.

Specific examples of the aromatic tertiary amine high-molecularcompounds having a repeating unit represented by formula (VII) includethe compounds described in International Publication No. 2005/089024.

Also preferred as a hole-transporting compound is a conductive polymer(PEDOT/PSS) obtained by polymerizing 3,4-ethylenedioxythiophene, whichis a derivative of polythiophene, in high-molecular poly(styrenesulfonicacid). This polymer may have been modified by capping the ends thereofwith a methacrylate or the like.

The hole-transporting compound may be the crosslinkable polymer whichwill be described later in the section [Hole Transport Layer]. In thecase of using the crosslinkable polymer, the same method for filmformation may be used.

The concentration of the hole-transporting compound in the compositionfor hole injection layer formation is not limited unless the effects ofthe invention are considerably lessened. However, from the standpoint ofthe evenness of film thickness, the lower limit thereof is generallypreferably 0.01% by mass, more preferably 0.1% by mass, even morepreferably 0.5% by mass. The upper limit thereof is generally preferably70% by mass, more preferably 60% by mass, even more preferably 50% bymass.

By regulating the concentration of the hole-transporting compound so asto be not higher than the upper limit, thickness unevenness can beprevented from occurring. By regulating the concentration thereof so asto be not lower than the lower limit, a hole injection layer having nodefect is formed.

(Electron-Accepting Compound)

It is preferred that the composition for hole injection layer formationshould contain an electron-accepting compound as a constituent materialfor the hole injection layer.

The electron-accepting compound preferably is a compound which hasoxidizing ability and has the ability to accept one electron from thehole-transporting compound described above. Specifically, compoundshaving an electron affinity of 4 eV or higher are preferred, andcompounds having an electron affinity of 5 eV or higher are morepreferred.

Examples of such electron-accepting compounds include one or morecompounds selected from the group consisting of triarylboron compounds,metal halides, Lewis acids, organic acids, onium salts, salts of anarylamine with a metal halide, and salts of an arylamine with a Lewisacid.

More specifically, examples thereof include onium salts substituted withorganic groups, such as 4-isopropyl-4′-methyldiphenyliodoniumtetrakis(pentafluorophenyl)borate and triphenylsulfoniumtetrafluoroborate (International Publication No. 2005/089024); inorganiccompounds having a high valence, such as iron(III) chloride(JP-A-11-251067) and ammonium peroxodisulfate; cyano compounds such astetracyanoethylene; aromatic boron compounds such astris(pentafluorophenyl)borane (JP-A-2003-31365); fullerene derivatives;iodine; and sulfonic acid ions such as poly(styrenesulfonic acid) ions;alkylbenzenesulfonic acid ions, and camphorsulfonic acid ions.

These electron-accepting compounds oxidize the hole-transportingcompound and can thereby improve the conductivity of the hole injectionlayer.

In the hole injection layer or in the composition for hole injectionlayer formation, the content of the electron-accepting compound isgenerally preferably 0.1% by mole or higher, more preferably 1% by moleor higher, based on the hole-transporting compound. The content thereofis generally preferably 100% by mole or lower, more preferably 40% bymole or lower.

(Other Constituent Materials)

Besides the hole-transporting compound and electron-accepting compounddescribed above, other ingredients may be incorporated as materials forthe hole injection layer unless the incorporation thereof considerablylessens the effects of the invention.

Examples of the other ingredients include various luminescent materials,electron-transporting compounds, binder resins, and applicabilityimprovers. One of such other ingredients may be used alone, or two ormore thereof may be used in any desired combination and proportion.

(Solvent)

It is preferred that the solvent(s) contained in the composition for usein hole injection layer formation by a wet film formation method shouldinclude at least one solvent in which the constituent materials for thehole injection layer described above can dissolve.

The boiling point of this solvent is generally preferably 110° C. orhigher, more preferably 140° C. or higher. In particular, a solventhaving a boiling point which is 200° C. or higher and is 400° C. orlower, especially 300° C. or lower, is preferred.

By using a solvent having a boiling point not lower than the lowerlimit, a moderate drying rate is attained and satisfactory film qualityis obtained. On the other hand, use of a solvent having a boiling pointnot higher than the higher limit eliminates the necessity of using ahigh temperature in the drying step and can prevent the drying fromadversely affecting other layers or the substrate.

Examples of the solvent include ethers, esters, aromatic hydrocarbons,and amides. Dimethyl sulfoxide and the like are also usable. Specificexamples of these solvents are as explained above.

One of these solvents may be used alone, or two or more thereof may beused in any desired combination and proportion.

(Methods of Film Formation)

After the composition for hole injection layer formation has beenprepared, this composition is applied, by a wet process, to the layer(usually, the anode 2) which is located on the outer surface of thebase, and the resultant coating film is dried. Thus, a hole injectionlayer 3 is formed.

The temperature to be used in the application step is preferably 10° C.or higher and is preferably 50° C. or lower, from the standpoint ofpreventing crystals from generating in the composition and therebycausing film defects.

The relative humidity in the application step is not limited unless theeffects of the invention are considerably lessened. However, therelative humidity is generally preferably 0.01 ppm or higher and isgenerally preferably 80% or less.

After the application, the film of the composition for hole injectionlayer formation is dried usually by heating, etc. Examples of means forheating usable in the heating step include a clean oven, hot plate,infrared rays, halogen lamp heater, and irradiation with microwaves.

Of these, a clean oven and a hot plate are preferred from the standpointof evenly heating the whole film.

With respect to heating temperature in the heating step, it is preferredto heat the film at a temperature not lower than the boiling point ofthe solvent used in the composition for hole injection layer formation,unless this drying considerably lessens the effects of the invention.

In the case where the solvent used for hole injection layer formation isa mixed solvent including two or more solvents, it is preferred to heatthe film at a temperature not lower than the boiling point of at leastone solvent contained in the mixed solvent. When an increase in theboiling point of solvents is taken into account, it is preferred thatthe temperature to be used in the heating step should be 120° C. to 410°C.

Heating period in the heating step is not limited so long as the heatingtemperature is not lower than the boiling point of the solvent of thecomposition for hole injection layer formation and the coating film isnot sufficiently insolubilized. However, the heating period ispreferably from 10 seconds to 180 minutes.

By regulating the heating period so as to be not longer than the upperlimit, components of other layers can be prevented from diffusing. Byregulating the heating period so as to be not shorter than the lowerlimit, the hole injection layer can be prevented from beinginhomogeneous. Heating may be conducted two times.

<Formation of Hole Injection Layer by Vacuum Deposition>

In the case where a hole injection layer 3 is to be formed by vacuumdeposition, one or more constituent materials (e.g., thehole-transporting compound and electron-accepting compound describedabove) for the hole injection layer 3 are placed in one or morecrucibles disposed within a vacuum vessel (when two or more materialsare used, the materials are placed in respective crucibles). The insideof the vacuum vessel is evacuated with an appropriate vacuum pump toabout 10⁻⁴ Pa, and the crucibles are then heated (when two or morematerials are used, the respective crucibles are heated) to vaporize thematerials while controlling vaporization amount (when two or morematerials are used, the materials are vaporized while independentlycontrolling the amounts of the materials being vaporized) to form a holeinjection layer 3 on the anode 2 of a substrate placed so as to face thecrucibles.

Incidentally, in the case where two or more materials are used, use maybe made of a method in which a mixture of these materials is placed in acrucible, heated, and vaporized to form a hole injection layer 3.

The degree of vacuum during the deposition is not limited unless theeffects of the invention are considerably lessened. However, the degreeof vacuum is generally preferably 0.1×10⁻⁶ Torr (0.13×10⁻⁴ Pa) orhigher, and is generally preferably 9.0×10⁻⁶ Torr (12.0×10⁻⁴ Pa) orlower.

The rate of deposition is not limited unless the effects of theinvention are considerably lessened. However, the rate of deposition isgenerally preferably 0.1 Å/sec or higher, and is generally preferably5.0 Å/sec or lower.

Film formation temperature during the deposition is not limited unlessthe effects of the invention are considerably lessened. However, thetemperature is preferably 10° C. or higher and is preferably 50° C. orlower.

[Hole Transport Layer]

Methods for forming the hole transport layer 4 according to theinvention are not particularly limited, and either a vacuum depositionmethod or a wet film formation method may be used. However, from thestandpoint of diminishing dark spots, it is preferred to form the holetransport layer 4 by a wet film formation method.

In the case where there is a hole injection layer, a hole transportlayer 4 can be formed on the hole injection layer 3. When there is nohole injection layer 3, then a hole transport layer 4 can be formed onthe anode 2. The organic electroluminescent element of the invention mayhave a configuration in which the hole transport layer has been omitted.

For forming the hole transport layer 4, it is preferred to use amaterial which has high hole-transporting properties and can efficientlytransport injected holes. In order for a material to have suchproperties, it is preferred that the material should have a lowionization potential, be highly transparent to visible light, and have ahigh hole mobility and excellent stability, and that impuritiesfunctioning as a trap do not generate during production of the materialor during use.

Furthermore, since the hole transport layer 4 is in contact with theluminescent layer 5 in many cases, it is preferred that the materialconstituting the hole transport layer 4 should not function to causeextinction of luminescence from the luminescent layer 5 or to form anexciplex with the luminescent layer 5 and thereby reduce efficiency.

As such a material for the hole transport layer 4, use may be made ofmaterials which have conventionally been used as constituent materialsfor hole transport layers. Examples thereof include the materialsenumerated above as examples of the hole-transporting compound to beused in the hole injection layer 3 described above.

Examples thereof further include arylamine derivatives, fluorenederivatives, Spiro derivatives, carbazole derivatives, pyridinederivatives, pyrazine derivatives, pyrimidine derivatives, triazinederivatives, quinoline derivatives, phenanthroline derivatives,phthalocyanine derivatives, porphyrin derivatives, silole derivatives,oligothiophene derivatives, fused-ring aromatic derivatives, and metalcomplexes.

Examples thereof furthermore include polyvinylcarbazole derivatives,polyarylamine derivatives, polyvinyltriphenylamine derivatives,polyfluorene derivatives, polyarylene derivatives, poly(arylene ethersulfone) derivatives containing tetraphenylbenzidine,polyarylenevinylene derivatives, polysiloxane derivatives, polythiophenederivatives, and poly(p-phenylenevinylene) derivatives.

These derivatives may be any of alternating copolymers, random polymers,block polymers, and graft copolymers. Furthermore, the derivatives maybe high-molecular compounds in which the main chain has one or morebranches and which have three or more ends, or may be the so-calleddendrimers.

Preferred of those are polyarylamine derivatives and polyarylenederivatives.

The polyarylamine derivatives preferably are polymers containing arepeating unit represented by the following general formula (VIII).Especially preferred are polymers each comprising repeating unitsrepresented by the following general formula (VIII). In this case, sucha polymer may be one in which the repeating units differ in Ar^(a) orAr^(b).

In general formula (VIII), Ar^(a) and Ar^(b) each independentlyrepresent an aromatic hydrocarbon group or aromatic heterocyclic groupwhich may have a substituent.

Examples of the aromatic hydrocarbon group which may have a substituentinclude groups derived from 6-membered monocycles or di- to pentacyclicfused rings, such as a benzene ring, naphthalene ring, anthracene ring,phenanthrene ring, perylene ring, tetracene ring, pyrene ring,benzpyrene ring, chrysene ring, triphenylene ring, acenaphthene ring,fluoranthene ring, and fluorene ring. Examples thereof further includegroups each made up of two or more rings selected from these rings andlinked together through a direct bond.

Examples of the aromatic heterocyclic group which may have a substituentinclude groups derived from 5- or 6-membered monocycles or di- totetracyclic fused rings, such as a furan ring, benzofuran ring,thiophene ring, benzothiophene ring, pyrrole ring, pyrazole ring,imidazole ring, oxadiazole ring, indole ring, carbazole ring,pyrroloimidazole ring, pyrrolopyrazole ring, pyrrolopyrrole ring,thienopyrrole ring, thienothiophene ring, furopyrrole ring, furofuranring, thienofuran ring, benzisoxazole ring, benzisothiazole ring,benzimidazole ring, pyridine ring, pyrazine ring, pyridazine ring,pyrimidine ring, triazine ring, quinoline ring, isoquinoline ring,cinnoline ring, quinoxaline ring, phenanthridine ring, benzimidazolering, perimidine ring, quinazoline ring, quinazolinone ring, and azulenering. Examples thereof further include groups each made up of two ormore rings selected from these rings and linked together through adirect bond.

From the standpoints of solubility and heat resistance, it is preferredthat Ar^(a) and Ar^(b) should each independently be a group derived froma ring selected from the group consisting of a benzene ring, naphthalenering, anthracene ring, phenanthrene ring, triphenylene ring, pyrenering, thiophene ring, pyridine ring, and fluorene ring, or be a groupmade up of two or more benzene rings linked together [e.g., a biphenylgroup (biphenylene group) and a terphenyl group (terphenylene group)].

Preferred of these are a group derived from a benzene ring (phenylgroup), a group made up of two benzene rings linked together (biphenylgroup), and a group derived from a fluorene ring (fluorenyl group).

Examples of the substituents which may be possessed by the aromatichydrocarbon groups and aromatic heterocyclic groups represented byAr^(a) and Ar^(b) include alkyl groups, alkenyl groups, alkynyl groups,alkoxy groups, aryloxy groups, alkoxycarbonyl groups, dialkylaminogroups, diarylamino groups, acyl groups, halogen atoms, haloalkylgroups, alkylthio groups, arylthio groups, silyl, siloxy, cyano,aromatic hydrocarbon ring groups, and aromatic heterocyclic groups.

Examples of the polyarylene derivatives include polymers having arepeating unit including an arylene group, such as an aromatichydrocarbon group or an aromatic heterocyclic group, that may havesubstituents shown above as examples with regard to the Ar^(a) andAr^(b).

It is preferred that the polyarylene derivatives should be polymershaving repeating units of the following general formula (IX-1) and/orthe following formula (IX-2).

In general formula (IX-1), R^(a), R^(b), R^(c), and R^(d) eachindependently represent an alkyl group, alkoxy group, phenylalkyl group,phenylalkoxy group, phenyl group, phenoxy group, alkylphenyl group,alkoxyphenyl group, alkylcarbonyl group, alkoxycarbonyl group, orcarboxy group. Symbols t and s each independently represent an integerof 0-3. When t or s is 2 or larger, then the multiple R^(a)s or R^(b)scontained in each molecule may be the same or different, and adjacentR^(a)s or R^(b)s may have been bonded to each other to form a ring.

In general formula (IX-2), R^(e) and R^(f) each independently have thesame meaning as the R^(a), R^(b), R^(c), or R^(d) contained in generalformula (IX-1). Symbols r and u each independently represent an integerof 0-3. When r or u is 2 or larger, then the multiple R^(e)s and R^(f)scontained in each molecule may be the same or different, and adjacentR^(e)s or R^(f)s may have been bonded to each other to form a ring. Xrepresents an atom or a group of atoms as a component of thefive-membered ring or six-membered ring.

Examples of X include —O—, —BR¹⁰³—, —NR¹⁰³—, —SiR¹⁰³ ₂—, —PR¹⁰³—,—SR¹⁰³—, —CR¹⁰³ ₂—, and a group made up of these atoms or groups bondedtogether. R¹⁰³ represents a hydrogen atom or any desired organic group.The term “organic group” in the invention means a group containing atleast one carbon atom.

It is also preferred that the polyarylene derivatives should have arepeating unit represented by the following general formula (IX-3)besides the repeating units of general formula (IX-1) and/or generalformula (IX-2).

In general formula (IX-3), Ar^(c) to Ar′ each independently represent anaromatic hydrocarbon group or aromatic heterocyclic group which may havea substituent. Symbols v and w each independently represent 0 or 1.

Examples of Ar^(c) to Ar^(j) are the same as the examples of the Ar^(a)and Ar^(b) contained in general formula (VIII).

Examples of general formulae (IX-1) to (IX-3), examples of thepolyarylene derivatives, etc. include the examples given inJP-A-2008-98619.

In the case where the hole transport layer 4 is to be formed by a wetfilm formation method, a composition for hole transport layer formationis prepared, subsequently formed into a film by a wet process, and thenheated and dried, as in the formation of the hole injection layer 3.

The composition for hole transport layer formation contains a solventbesides the hole-transporting compound described above. The solvent tobe used may be the same as the solvent used in the composition for holeinjection layer formation. Film formation conditions, heating/dryingconditions, and the like also are the same as in the formation of thehole injection layer 3.

Also in the case where a hole transport layer is to be formed by avacuum deposition method, conditions for the deposition and otherconditions may be the same as in the formation of the hole injectionlayer 3.

The hole transport layer 4 may contain various luminescent materials,electron-transporting compounds, binder resins, applicability improvers,etc., besides the hole-transporting compound.

The hole transport layer 4 may also be a layer formed by crosslinking acrosslinkable compound. The crosslinkable compound is a compound whichhas a crosslinkable group and forms a network high-molecular compoundthrough crosslinking.

Examples of the crosslinkable group include groups derived from cyclicethers, such as oxetane and epoxy, groups derived from an unsaturateddouble bond, such as vinyl, trifluorovinyl, styryl, acryloyl,methacryloyl, and cinnamoyl; and groups derived from benzocyclobutene.

The crosslinkable compound may be any of a monomer, an oligomer, and apolymer. One crosslinkable compound may be contained alone, or two ormore crosslinkable compounds may be contained in any desired combinationand proportion.

As the crosslinkable compound, it is preferred to use ahole-transporting compound having a crosslinkable group. Examples of thehole-transporting compound include nitrogen-containing aromatic compoundderivatives such as pyridine derivatives, pyrazine derivatives,pyrimidine derivatives, triazine derivatives, quinoline derivatives,phenanthroline derivatives, carbazole derivatives, phthalocyaninederivatives, and porphyrin derivatives, triphenylamine derivatives,silole derivatives, oligothiophene derivatives, fused-ring aromaticderivatives, and metal complexes.

Preferred of these are nitrogen-containing aromatic derivatives such aspyridine derivatives, pyrazine derivatives, pyrimidine derivatives,triazine derivatives, quinoline derivatives, phenanthroline derivatives,and carbazole derivatives, triphenylamine derivatives, silolederivatives, fused-ring aromatic derivatives, and metal complexes. Inparticular, triphenylamine derivatives are preferred.

Examples of the crosslinkable compound include those hole-transportingcompounds in which a crosslinkable group has been bonded to the mainchain or a side chain thereof. It is especially preferred that acrosslinkable group should have been bonded to the main chain through alinking group such as, for example, an alkylene group.

Furthermore, it is especially preferred that the hole-transportingcompound should be a polymer containing a repeating unit having acrosslinkable group, and should be a polymer having a repeating unitrepresented by any of general formulae (VIII) and (IX-1) to (IX-3) towhich a crosslinkable group has been bonded either directly or through alinking group.

For forming a hole transport layer 4 through crosslinking of acrosslinkable compound, use is generally made of a method which includesdissolving or dispersing the crosslinkable compound in a solvent toprepare a composition for hole transport layer formation, forming thiscomposition into a film by a wet process, and crosslinking thecrosslinkable compound.

The composition for hole transport layer formation may contain anadditive which accelerates the crosslinking reaction, besides thecrosslinkable compound. Examples of the additive which accelerates thecrosslinking reaction include polymerization initiators such asalkylphenone compounds, acylphosphine oxide compounds, metallocenecompounds, oxime ester compounds, azo compounds, and onium salts;polymerization accelerators; and photosensitizers such as fused-ringhydrocarbons, porphyrin compounds, and diaryl ketone compounds.

The composition may further contain an applicability improver such as aleveling agent or an antifoamer, an electron-accepting compound, abinder resin, and the like.

The content of the crosslinkable compound in the composition for holetransport layer formation is generally preferably 0.01% by mass orhigher, more preferably 0.05% by mass or higher, even more preferably0.1% by mass or higher. The content thereof is generally preferably 50%by weight or lower, more preferably 20% by weight or lower, even morepreferably 10% by weight or lower.

It is preferred that the composition for hole transport layer formationwhich contains a crosslinkable compound in that concentration should beapplied to the layer to be an underlying layer (usually, the holeinjection layer 3) to form a film and the crosslinkable compound shouldbe thereafter crosslinked by means of heating and/or irradiation withactinic energy, such as light, to thereby form a network high-molecularcompound.

Conditions including temperature and humidity for the film formation arethe same as in the wet film formation for forming the hole injectionlayer 3.

Techniques for heating to be conducted after film formation are notparticularly limited. With respect to heating temperature conditions,the temperature is generally preferably 120° C. or higher and is morepreferably 400° C. or lower.

The heating period is generally preferably 1 minute or longer and ismore preferably 24 hours or shorter.

Although methods for heating are not particularly limited, use may bemade, for example, of a method in which the multilayer structure havingthe layer formed is put on a hot plate or heated in an oven. Forexample, use can be made of conditions under which the multilayerstructure is heated on a hot plate at 120° C. or higher for 1 minute orlonger.

In the case of irradiation with actinic energy such as light, examplesof methods therefor include a method in which an ultraviolet, visible,or infrared light source, e.g., an ultrahigh-pressure mercury lamp,high-pressure mercury lamp, halogen lamp, or infrared lamp, is used todirectly irradiate the layer and a method in which a mask aligner orconveyor type irradiator that has any of those light sources builttherein is used to irradiate the layer.

With respect to irradiation with actinic energy other than light,examples of methods therefor include a method in which an apparatus forirradiating with microwaves generated by a magnetron, i.e., theso-called electronic oven, is used for the irradiation.

With respect to irradiation period, it is preferred to set conditionsnecessary for reducing the solubility of the film. However, theirradiation period is generally preferably 0.1 sec or longer and is morepreferably 10 hours or shorter.

Heating and irradiation with actinic energy, e.g., light, may beconducted alone or in combination. In the case where heating and theirradiation are conducted in combination, the sequence of performingthese is not particularly limited.

The thickness of the hole transport layer 4 thus formed is generallypreferably 5 nm or more, more preferably 10 nm or more, and is generallypreferably 300 nm or less, more preferably 100 nm or less.

[Luminescent Layer]

A luminescent layer 5 is usually disposed on the hole injection layer 3.The luminescent layer 5, for example, is a layer containing theluminescent material described above. The luminescent layer 5 is a layerwhich, between the electrodes placed in an electric field, is excited byrecombination of holes injected from the anode 2 through the holeinjection layer 3 with electrons injected from the cathode 9 through theelectron transport layer 7 and which thus functions as the mainluminescent source.

It is preferred that the luminescent layer 5 should contain aluminescent material (dopant) and one or more host materials. It is morepreferred that the luminescent layer 5 should contain the chargetransport material of the invention as a host material.

Although the luminescent layer 5 may be formed by a vacuum depositionmethod, it is especially preferred that the luminescent layer 5 shouldbe a layer formed from the composition for organic electroluminescentelements of the invention by a wet film formation method.

As stated above, the wet film formation method is a technique forforming a film from a solvent-containing composition by spin coating,spray coating, dip coating, die coating, flexographic printing, screenprinting, ink-jet printing, etc.

The luminescent layer 5 may contain other materials or ingredients solong as the performance of the invention is not impaired thereby.

In general, organic electroluminescent elements having a smallerthickness of films interposed between the electrodes have a strongereffective electric field when the same materials are used. As a result,a larger amount of current is injected and the operating voltagedecreases. Consequently, the smaller the total thickness of filmsinterposed between the electrodes, the lower the operating voltage ofthe organic electroluminescent element. However, too small thicknessesthereof may result in short-circuiting due to projections attributableto an electrode, e.g., ITO. Some degree of film thickness is thereforenecessary.

In the invention, when the organic electroluminescent element hasorganic layers such as the hole injection layer 3 and the electrontransport layer 7 which will be described later, besides the luminescentlayer 5, then the total thickness of the luminescent layer 5 and theother organic layers including the hole injection layer 3 and theelectron transport layer 7 is generally preferably 30 nm or more, morepreferably 50 nm or more, even more preferably 100 nm or more. The upperlimit of the total thickness thereof is generally preferably 1,000 nm,more preferably 500 nm, even more preferably 300 nm.

In the case where a layer other than the luminescent layer 5, e.g., thehole injection layer 3 or the electron injection layer 8 which will bedescribed later, has high conductivity, an increased amount of chargesare injected into the luminescent layer 5. It is therefore possible tolower the operating voltage while maintaining some degree of total filmthickness, by increasing the thickness of, for example, the holeinjection layer 3 and reducing the thickness of the luminescent layer 5.

Consequently, the thickness of the luminescent layer 5 is generallypreferably 10 nm or more, more preferably 20 nm or more. The thicknessthereof is generally preferably 300 nm or less, more preferably 200 nmor less.

In the case where the element of the invention has the luminescent layer5 as the only layer interposed between the anode and the cathode, thethickness of this luminescent layer 5 is generally preferably 30 nm ormore, more preferably 50 nm or more. The thickness thereof is generallypreferably 500 nm or less, more preferably 300 nm or less.

[Hole Blocking Layer]

A hole blocking layer 6 may be disposed between the luminescent layer 5and the electron injection layer 8 which will be described later. Thehole blocking layer 6 is a layer superposed on the luminescent layer 5so as to be in contact with that interface of the luminescent layer 5which faces the cathode 9.

This hole blocking layer 6 serves to block holes sent from the anode 2and prevent the holes from reaching the cathode 9, and further serves toefficiently transport, toward the luminescent layer 5, electronsinjected from the cathode 9.

Examples of properties which are required of the material constitutingthe hole blocking layer 6 include a high electron mobility and a lowhole mobility, a large energy gap (difference between HOMO and LUMO),and a high excited-triplet level (Ti).

Examples of materials for the hole blocking layer which satisfy suchrequirements include metal complexes such as mixed-ligand complexes,e.g., bis(2-methyl-8-quinolinolato)(phenolato)aluminum andbis(2-methyl-8-quinolinolato)(triphenylsilanolato)aluminum, anddinuclear metal complexes such asbis(2-methyl-8-quinolato)aluminum-μ-oxobis(2-methyl-8-quinolilato)aluminum,styryl compounds such as distyrylbiphenyl derivatives (JP-A-11-242996),triazole derivatives such as3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(JP-A-7-41759), and phenanthroline derivatives such as bathocuproine(JP-A-10-79297).

Furthermore, the compound having at least one pyridine ring substitutedin the 2-, 4-, and 6-positions which is described in InternationalPublication No. 2005/022962 is also preferred as a material for the holeblocking layer 6.

One material only may be used for forming the hole blocking layer 6, ortwo or more materials may be used for forming the layer 6 in any desiredcombination and proportion.

Methods for forming the hole blocking layer 6 are not limited.Consequently, the hole blocking layer 6 can be formed by a wet filmformation method, vapor deposition method, or another method.

The thickness of the hole blocking layer 6 is not limited unless theeffects of the invention are considerably lessened. However, thethickness thereof is generally preferably 0.3 nm or more, morepreferably 0.5 nm or more, and is generally preferably 100 nm or less,more preferably 50 nm or less.

[Electron Transport Layer]

An electron transport layer 7 may be disposed between the luminescentlayer 5 and the electron injection layer 8 which will be describedlater.

The electron transport layer 7 is disposed for the purpose of furtherimproving the luminescent efficiency of the element, and is constitutedof one or more compounds which, between the electrodes placed in anelectric field, can efficiently transport, toward the luminescent layer5, electrons injected from the cathode 9.

As electron-transporting compounds for the electron transport layer 7,use is generally made of compounds which attain a high efficiency ofelectron injection from the cathode 9 or electron injection layer 8 andwhich have a high electron mobility and can efficiently transportinjected electrons.

Examples of compounds satisfying such requirements include metalcomplexes such as an aluminum complex of 8-hydroxyquinoline(JP-A-59-194393), metal complexes of 10-hydroxybenzo[h]quinoline,oxadiazole derivatives, distyrylbiphenyl derivatives, silolederivatives, 3-hydroxyflavone metal complexes, 5-hydroxyflavone metalcomplexes, benzoxazole metal complexes, benzthiazole metal complexes,trisbenzimidazolylbenzene (U.S. Pat. No. 5,645,948), quinoxalinecompounds (JP-A-6-207169), phenanthroline derivatives (JP-A-5-331459),2-t-butyl-9,10-N,N′-dicyanoanthraquinonediimine, n-type amorphoussilicon hydride carbide, n-type zinc sulfide, and n-type zinc selenide.

One material only may be used for forming the electron transport layer7, or two or more materials may be used for forming the layer 7 in anydesired combination and proportion.

Methods for forming the electron transport layer 7 are not limited.Consequently, the electron transport layer 7 can be formed by a wet filmformation method, vapor deposition method, or another method.

The thickness of the electron transport layer 7 is not limited unlessthe effects of the invention are considerably lessened. However, thethickness thereof is generally preferably 1 nm or more, more preferably5 nm or more, and is generally preferably 300 nm or less, morepreferably 100 nm or less.

[Electron Injection Layer]

The electron injection layer 8 serves to efficiency inject, into theluminescent layer 5, electrons injected from the cathode 9. From thestandpoint of efficiently injecting electrons, it is preferred that thematerial constituting the electron injection layer 8 should be a metalhaving a low work function.

Examples thereof include alkali metals such as sodium and cesium andalkaline earth metals such as barium and calcium. The thickness of thelayer is generally preferably 0.1 nm or more and is more preferably 5 nmor less.

Furthermore, doping of an organic electron transport compoundrepresented by a nitrogen-containing heterocyclic compound, e.g.,bathophenanthroline, or a metal complex, e.g., an aluminum complex of8-hydroxyquinoline, with an alkali metal such as sodium, potassium,cesium, lithium, or rubidium (described in JP-A-10-270171,JP-A-2002-100478, JP-A-2002-100482, etc.) is preferred because thisdoping improves suitability for electron injection and transport andenables the layer to combine the improved suitability and excellent filmquality.

The thickness of the film in this case is generally preferably 5 nm ormore, more preferably 10 nm or more, and is generally preferably 200 nmor less, more preferably 100 nm or less.

One material only may be used for forming the electron injection layer8, or two or more materials may be used for forming the layer 8 in anydesired combination and proportion.

Methods for forming the electron injection layer 8 are not limited.Consequently, the electron injection layer 8 can be formed by a wet filmformation method, vapor deposition method, and other methods.

[Cathode]

The cathode 9 serves to inject electrons into a layer located on theluminescent layer 5 side (e.g., the electron injection layer 8 or theluminescent layer 5).

As the material of the cathode 9, the materials usable for the anode 2can be used. However, metals having a low work function are preferredfrom the standpoint of efficiently injecting electrons.

Examples thereof include suitable metals such as tin, magnesium, indium,calcium, aluminum, and silver and alloys of these. Specific examplesthereof include electrodes of alloys having a low work function, such asmagnesium-silver alloys, magnesium-indium alloys, and aluminum-lithiumalloys.

One material only may be used for forming the cathode 9, or two or morematerials may be used for forming the cathode 9 in any desiredcombination and proportion.

The thickness of the cathode 9 is generally the same as that of theanode 2.

For the purpose of protecting the cathode 9 made of a metal having a lowwork function, a layer of a metal which has a high work function and isstable to the air may be formed on the cathode 9. This layer formationis preferred because the stability of the element is enhanced thereby.

For that purpose, metals such as, for example, aluminum, silver, copper,nickel, chromium, gold, and platinum are used. One of these materialsmay be used alone, or two or more thereof may be used in any desiredcombination and proportion.

[Other Layers]

The organic electroluminescent element according to the invention mayhave other configurations unless the configurations depart from thespirit of the invention. For example, unless the performance of theelement is impaired, the element may have any desired layer other thanthe layers described above, between the anode 2 and the cathode 9, orany layer may have been omitted.

[Electron Blocking Layer]

Examples of the layers which may be possessed include an electronblocking layer.

The electron blocking layer is disposed between the hole injection layer3 or hole transport layer 4 and the luminescent layer 5. The electronblocking layer serves to block electrons sent from the luminescent layer5 and prevent the electrodes from reaching the hole injection layer 3.The electron blocking layer thus functions to heighten the probabilityof recombination of holes with electrons within the luminescent layer 5and to confine the resultant excitons in the luminescent layer 5. Theelectron blocking layer further has the function of efficientlytransporting, toward the luminescent layer 5, holes injected from thehole injection layer 3.

To dispose the electron blocking layer is effective especially when aphosphorescent material or a blue luminescent material is used as aluminescent material.

Examples of properties which are required of the electron blocking layerinclude high hole-transporting properties, a large energy gap(difference between HOMO and LUMO), and a high excited-triplet level(T1).

Furthermore, in the invention, when the luminescent layer 5 is to beformed by a wet film formation method, the electron blocking layer alsois required to have suitability for the wet film formation. Examples ofmaterials usable for forming such an electron blocking layer includecopolymers of dioctylfluorene and triphenylamine which are representedby F8-TFB (International Publication No. 2004/084260).

One material only may be used for forming the electron blocking layer,or two or more materials may be used for forming the layer in anydesired combination and proportion.

Methods for forming the electron blocking layer are not limited.Consequently, the electron blocking layer can be formed by a wet filmformation method, vapor deposition method, or another method.

Furthermore, to interpose an ultrathin insulating film (0.1-5 nm) madeof, for example, lithium fluoride (LiF), magnesium fluoride (MgF₂),lithium oxide (Li₂O), and cesium(II) carbonate (CsCO₃) at the interfacebetween the cathode 9 and the luminescent layer 5 or electron transportlayer 7 is an effective technique for improving the efficiency of theelement (see, for example, Applied Physics Letters, Vol. 70, p. 152,1997; JP-A-10-74586; IEEE Transactions on Electron Devices, Vol. 44, p.1245, 1997; and SID 04 Digest, p. 154).

The configuration of the organic electroluminescent element of theinvention should not be construed as being limited to the configurationdescribed above, and the sequence of layer superposition can be changed.Specifically, the element may have a structure including a substrate 1and, superposed thereon in the following order, a cathode 9, electroninjection layer 8, electron transport layer 7, hole blocking layer 6,luminescent layer 5, hole transport layer 4, hole injection layer 3, andanode 2.

It is also possible to constitute an organic electroluminescent elementaccording to the invention by superposing the constituent elements otherthan the substrate between two substrates, at least one of which istransparent.

A structure composed of a stack of stages each composed of constituentelements other than substrates (luminescent units) (i.e., a structurecomposed of a plurality of stacked luminescent units) is also possible.

In this case, when a carrier generation layer (CGL) containing, forexample, vanadium pentoxide (V₂O₅) is disposed in place of theinterfacial layers located between the stages (i.e., between theluminescent units) (when the anode is ITO and the cathode is aluminum,the interfacial layers are these two layers), then the barrier betweenthe stages is reduced. This configuration is more preferred from thestandpoints of luminescent efficiency and operating voltage.

Furthermore, the organic electroluminescent element according to theinvention may be configured so as to be a single organicelectroluminescent element, or may be applied to a configuration inwhich a plurality of organic electroluminescent elements have beendisposed in an array arrangement. The organic electroluminescent elementmay also be applied to a configuration in which anodes and cathodes havebeen disposed in an X-Y matrix arrangement.

Each of the layers described above may contain ingredients other thanthose described above, unless the effects of the invention areconsiderably lessened thereby.

<Organic EL Display and Organic EL Lighting>

The organic EL display and organic EL lighting of the invention areequipped with the organic electroluminescent element of the inventiondescribed above. The types and structures of the organic EL display andorganic EL lighting of the invention are not particularly limited, andcan be fabricated using the organic electroluminescent element of theinvention according to ordinary methods.

For example, the organic EL display and organic EL lighting of theinvention can be formed by the methods described in Y uki EL Dispurei(Ohmsha, Ltd., published on Aug. 20, 2004, written by TOKITO Shizuo,ADACHI Chihaya, and MURATA Hideyuki).

EXAMPLES

The invention will be explained below in more detail by reference toExamples. However, the invention should not be construed as beinglimited to the following Examples, and the invention can be modified atwill unless the modifications depart from the spirit of the invention.

Synthesis of Compound 1 Synthesis of Compound 1

The starting compound (15.0 g; 37 mmol) was introduced into a 500-mLfour-necked flask, and nitrogen displacement was conducted for 30minutes. Into the reaction vessel was introduced 200 mL of anhydrousTHF. Thereafter, the solution was cooled to −80° C. A hexane solution ofn-BuLi (1.65 M; 24.0 mL) was added dropwise thereto over 30 minuteswhile taking care that the liquid temperature did not rise, and thismixture was reacted for 4 hours. Trimethoxyborane (11.8 g; 112 mmol) wasadded dropwise thereto over 10 minutes, and the resultant mixture wasreacted for 2 hours.

The reaction solution was warmed to room temperature and stirred for 30minutes. Two hundred milliliters of 1-N aqueous HCl solution was addedto the reaction solution, and this solution was stirred for further 30minutes. Five hundred milliliters of ethyl acetate was added to thereaction solution to extract the target substance with the organiclayer. Thereafter, the organic phase was washed with an aqueous sodiumchloride solution. The organic layer was dried with magnesium sulfateand then concentrated with an evaporator. The yellow solid obtained wassuspended in and washed with hexane to obtain compound 1 (15.2 g).

Synthesis of Compound 2

Toluene (204 mL), 2-M aqueous sodium carbonate solution (102 mL), andethanol (102 mL) were added to m-carbazolylphenylboronic acid (13.1 g;45.9 mmol) and bis(4-bromophenyl)amine (15.0 g; 45.9 mmol) in a nitrogenatmosphere, and nitrogen was passed for 10 minutes to conduct degassing.

Tetrakis(triphenylphosphine)palladium(0) (297 mg; 257 mol) was added tothe mixture, and the resultant mixture was stirred for 3 hours withrefluxing. After completion of the reaction, the reaction solution waspoured into water and extracted with toluene. The organic layer waswashed with purified water and dried with magnesium sulfate. Thereafter,the solvent was distilled off under reduced pressure. The residue waspurified by silica gel column chromatography to obtain compound 2 (13.4g). This compound had a mass spectrometric value of 488 (M⁺).

Synthesis of Compound 3

The compound 2 (3.5 g; 7.1 mmol), the compound 1 (5.2 g; 14.3 mol; 2MR), 122 mL of toluene, 88 mL of ethanol, and 62 mL of aqueous sodiumcarbonate solution were introduced into a 500-mL four-necked flask, andnitrogen bubbling was conducted at 60° C. for 1 hour.

Tetrakis(triphenylphosphine)palladium(0) (580 mg; 7 mol %) was added tothe reaction solution, and the mixture was refluxed for 3 hours. Aftercompletion of the reaction, the reaction solution was poured into waterand extracted with toluene. The organic layer was washed with purifiedwater and dried with magnesium sulfate. Thereafter, the solvent wasdistilled off under reduced pressure. The residue was purified by silicagel column chromatography to obtain compound 3 (5.11 g).

Synthesis of Compound 4

Toluene (176 mL), 2-M aqueous sodium carbonate solution (88 mL), andethanol (88 mL) were added to 3-biphenylboronic acid (18.3 g; 92.5 mmol)and 4-iodobromobenzene (24.9 g; 87.9 mmol) in a nitrogen atmosphere, andnitrogen was passed for 10 minutes to conduct degassing.

Tetrakis(triphenylphosphine)palladium(0) (1.5 g; 1.29 mmol) was added tothe mixture, and the resultant mixture was stirred for 3 hours withrefluxing. After completion of the reaction, the reaction solution waspoured into water and extracted with toluene.

The organic layer was washed with purified water and dried withmagnesium sulfate. Thereafter, the solvent was distilled off underreduced pressure. The residue was purified by silica gel columnchromatography to obtain compound 4 (22.6 g). This compound had a massspectrometric value of 308 (M⁺).

Synthesis of Compound I

The compound 3 (5.11 g; 7.0 mmol), the compound 4 (2.82 g; 2.5 mmol),NaOtBu (1.35 g; 8.8 mmol; 2 MR), and 100 mL of toluene were introducedinto a 300-mL four-necked flask, and nitrogen bubbling was conducted for30 minutes (solution A).

On the other hand, tri-t-butylphosphine (284 mg) was added to a toluenesolution (5 mL) of a tris(dibenzylideneacetone)dipalladium chloroformcomplex (181 mg), and the mixture was heated to 65° C. (solution B). Ina nitrogen stream, solution B was added to solution A, and this mixturewas reacted with heating and refluxing for 4 hours. The organic layerwas washed with purified water and dried with magnesium sulfate.Thereafter, the solvent was distilled off under reduced pressure. Theresidue was purified by silica gel column chromatography and sublimationpurification to obtain compound I (2.1 g).

<Measurement of Solubility in m-Xylene>

The compound I synthesized in [Synthesis of Compound I] above and thecomparative compounds X-A and X-B represented by the followingstructural formulae were examined for solubility in m-xylene. Theresults thereof are shown in Table 1.

TABLE 1 Concentration Glass transition 1.0 5.0 10 Compound temperaturemass % mass % mass % Example 1 I 127° C. + + + Comparative X-A 159° C. +− − Example 1 Comparative X-B 120° C. − − − Example 2 +: The compounddissolved. −: The compound remained undissolved, giving a suspension, orseparated out as crystals in 12 hours.

As shown in Table 1, the charge transport material of the invention wasascertained to have high solubility in the organic solvent.

Production of Organic Electroluminescent Element Example 1

An organic electroluminescent element of the structure shown in FIG. 1was produced in the following manner. A glass substrate 1 having a sizeof 17.5 mm×35 mm (thickness, 0.7 mm) was cleaned by subjecting thesubstrate to ultrasonic cleaning with an aqueous surfactant solution,rinsing with ultrapure water, ultrasonic cleaning with ultrapure water,and rinsing with ultrapure water in this order, subsequently dried bynitrogen blowing, and finally subjected to ultraviolet/ozone cleaning.

A transparent conductive film of indium-tin oxide (ITO) was deposited ina thickness of 150 nm on the glass substrate 1 (the film was depositedby sputtering; sheet resistivity, 15Ω), and this coated substrate wasprocessed by an ordinary technique of photolithography to pattern theconductive film into stripes having a width of 2 mm. Thus, an anode 2was formed.

The substrate 1 on which the anode 2 had been formed was cleaned bysubjecting the substrate to ultrasonic cleaning with acetone, rinsingwith pure water, and ultrasonic cleaning with isopropyl alcohol in thisorder, subsequently dried by nitrogen blowing, and finally subjected toultraviolet/ozone cleaning.

A composition for hole injection layer formation which includedhigh-molecular compound P-1 having a structure represented by thefollowing formula (weight-average molecular weight (MwA), 93,000;dispersity ratio, 1.69) as a polymeric material for constituting a holeinjection layer, compound A-1 having the structure represented by thefollowing formula as an electron-accepting compound and also as apolymerization initiator, and ethyl benzoate as a solvent was prepared.The concentrations of the high-molecular compound P-1 and the compoundA-1 in the composition were 2.0% by mass and 0.8% by mass, respectively.

This composition was applied on the anode 2 by spin coating in the airunder the conditions of a spinner rotation speed of 1,500 rpm and aspinner rotation period of 30 seconds. The coating film was heated at230° C. for 3 hours to thereby crosslink the high-molecular compound P-1and dry the coating film. Thus, an even thin film having a thickness of45 nm (hole injection layer 3) was formed.

Subsequently, a composition for hole transport layer formation whichincluded a high-molecular compound P-2 having a structure represented bythe following formula (weight-average molecular weight (MwB), 66,000;dispersity ratio, 1.56) as a polymeric material for constituting a holetransport layer and cyclohexylbenzene as a solvent was prepared. Theconcentration of the high-molecular compound P-2 in the composition was1.4% by mass.

This composition was applied on the hole injection layer 3 by spincoating in nitrogen under the conditions of a spinner rotation speed of1,500 rpm and a spinner rotation period of 30 seconds. The coating filmwas heated at 230° C. for 1 hour in nitrogen to thereby crosslink thehigh-molecular compound P-2 and dry the coating film. Thus, an even thinfilm having a thickness of 20 nm (hole transport layer 4) was formed.

Next, a composition for luminescent-layer formation which includedcompound C1 represented by the following formula and the compound Iobtained in Synthesis Example as charge-transporting compounds,phosphorescent metal complex D1, and cyclohexylbenzene as a solvent wasprepared. The concentrations of the compound C1, the compound I, and thephosphorescent metal complex D1 in the composition were 1.1% by mass,3.4% by mass, and 0.3% by mass, respectively.

This composition was applied on the hole transport layer 4 by spincoating in nitrogen under the conditions of a spinner rotation speed of1,500 rpm and a spinner rotation period of 30 seconds. The coating filmwas dried at 130° C. for 1 hour at a reduced pressure (0.1 MPa) tothereby dry the coating film. Thus, an even thin film having a thicknessof 50 nm (luminescent layer 5) was formed.

Here, the substrate on which the layers including the luminescent layer5 had been formed was transferred into a vacuum deposition apparatus,and the apparatus was evacuated to a degree of vacuum within theapparatus of at least 1.3×10⁻⁴ Pa. Thereafter, a layer of compound C2shown below was formed on the luminescent layer 5 by vacuum depositionto obtain a hole blocking layer 6. The rate of deposition was regulatedso as to be in the range of 1.4-1.5 Å/sec, and the layer was depositedin a thickness of 10 nm. The degree of vacuum during the deposition was1.3×10⁻⁴ Pa.

Subsequently, the aluminum 8-hydroxyquinoline complex (ET-1) shown belowwas heated and vapor-deposited on the hole blocking layer 6 to form anelectron transport layer 7. The degree of vacuum during the depositionwas regulated to 1.3×10⁻⁴ Pa, and the rate of deposition was regulatedso as to be in the range of 1.6-1.8 Å/sec. The layer was deposited in athickness of 30 nm.

Here, the element in which the layers including the vapor-depositedelectron transport layer 7 had been formed was temporarily taken out anddisposed in another vacuum deposition apparatus. A shadow mask in theform of stripes with a width of 2 mm was brought, as a mask for cathodedeposition, into close contact with the element so that these stripeswere perpendicular to the ITO stripes of the anode 2, and the apparatuswas evacuated to a degree of vacuum within the apparatus of at least2.3×10⁻⁴ Pa.

First, lithium fluoride (LiF) was deposited as an electron injectionlayer 8 in a thickness of 0.5 nm on the electron transport layer 7 at adeposition rate of 0.1 Å/sec using a molybdenum boat. The degree ofvacuum during the deposition was 2.6×10⁻⁴ Pa.

Next, aluminum was likewise heated using a molybdenum boat, and analuminum layer having a thickness of 80 nm was formed as a cathode 9while regulating the rate of deposition so as to be in the range of1.0-4.9 Å/sec. The degree of vacuum during the deposition was 2.6×10⁻⁴Pa. During the deposition of these two layers, the temperature of thesubstrate was kept at room temperature.

Subsequently, sealing was conducted in the following manner in order toprevent the element from being deteriorated by the action of atmosphericmoisture, etc. during storage.

In a gloved nitrogen box, a photocurable resin (30Y-437, manufactured byThreeBond Co., Ltd.) was applied in a width of about 1 mm to theperiphery of a glass plate having a size of 23 mm×23 mm, and a moisturegetter sheet (manufactured by Dynic Corp.) was disposed in a centralpart. The substrate on which the cathode had been formed was laminatedto the getter sheet so that the side having the deposited layers facedthe desiccant sheet. Thereafter, only the region where the photocurableresin had been applied was irradiated with ultraviolet light to cure theresin.

Thus, an organic electroluminescent element having a luminescent areawith a size of 2 mm×2 mm was obtained. This element had the followingluminescent characteristics. The operating voltage thereof at 1,000cd/m² was 7.9 V, and the luminescent efficiency thereof at 1,000 cd/m²was 40.0 cd/A. The operating voltage (V) thereof at 10 mA was 9.4 V.

Those results showed that the organic electroluminescent element of theinvention had a high luminescent efficiency.

Synthesis of Compound 11 Synthesis of Compound 5

Toluene (174 mL), 2-M aqueous sodium carbonate solution (181 mL), andethanol (88 mL) were added to 1-naphthylboronic acid (20.0 g; 116.3mmol) and 3-iodobromobenzene (36.2 g; 128 mmol) in a nitrogenatmosphere, and nitrogen was passed for 10 minutes to conduct degassing.

Tetrakis(triphenylphosphine)palladium(0) (1.34 g) was added to themixture, and the resultant mixture was stirred for 6 hours withrefluxing. After completion of the reaction, the reaction solution waspoured into water and extracted with toluene. The organic layer waswashed with purified water and dried with magnesium sulfate. Thereafter,the solvent was distilled off under reduced pressure. The residue waspurified by silica gel column chromatography to obtain compound 5 (26.7g).

Synthesis of Compound 6

In a nitrogen atmosphere, 353.7 mL of dehydrated THF was added to thecompound 5 (27.2 g; 96 mmol), and nitrogen was passed for 10 minutes toconduct degassing. The solution was cooled to −75° C. Thereafter, 72.0mL of a 1.6-M hexane solution of n-butyllithium was added dropwisethereto. After stirring for 1 hour at −75° C., trimethoxyborane (31.9 g;307 mmol) was added dropwise thereto.

The resultant mixture was stirred at −75° C. for 2 hours and then warmedto room temperature. To this solution was added 177 mL of 1-Nhydrochloric acid solution. This mixture was stirred for 30 minutes. Tothe resultant solution was added 101 mL of ethyl acetate. The organiclayer was washed with purified water and dried with magnesium sulfate.Thereafter, the solvent was distilled off under reduced pressure. Thus,compound 6 (29.8 g) was obtained.

Synthesis of Compound 7

Toluene (631.7 mL), 2-M aqueous sodium carbonate solution (327.8 mL),and ethanol (315.7 mL) were added to the compound 6 (29.8 g; 120 mmol)and 4-iodobromobenzene (40.78 g; 144 mmol) in a nitrogen atmosphere, andnitrogen was passed for 10 minutes to conduct degassing.

Tetrakis(triphenylphosphine)palladium(0) (2.01 g) was added to themixture, and the resultant mixture was stirred for 6 hours withrefluxing. After completion of the reaction, the reaction solution waspoured into water and extracted with toluene.

The organic layer was washed with purified water and dried withmagnesium sulfate. Thereafter, the solvent was distilled off underreduced pressure. The residue was purified by silica gel columnchromatography to obtain compound 7 (27.32 g).

Synthesis of Compound 8

Toluene (558.4 mL), 2-M aqueous sodium carbonate solution (278.7 mL),and ethanol (279.5 mL) were added to m-carbazolylphenylboronic acid(28.04 g; 98 mmol) and 4-bromoaniline (16.00 g; 93 mmol) in a nitrogenatmosphere, and nitrogen was passed for 10 minutes to conduct degassing.

Tetrakis(triphenylphosphine)palladium(0) (2.15 g) was added to themixture, and the resultant mixture was stirred for 6 hours withrefluxing. After completion of the reaction, the reaction solution waspoured into water and extracted with toluene.

The organic layer was washed with purified water and dried withmagnesium sulfate. Thereafter, the solvent was distilled off underreduced pressure. The residue was purified by silica gel columnchromatography to obtain compound 8 (27.37 g).

Into a 200-mL four-necked flask were introduced the compound 8 (5.0 g;615.0 mmol), the compound 7 (4.8 g; 13.5 mmol), NaOtBu (4.88 g; 50mmol), and 100 mL of toluene. Nitrogen bubbling was conducted for 30minutes (solution A).

On the other hand, tri-t-butylphosphine (121 mg) was added to a toluenesolution (6 mL) of a tris(dibenzylideneacetone)dipalladium chloroformcomplex (77 mg), and the mixture was heated to 65° C. (solution B).

In a nitrogen stream, solution B was added to solution A, and thismixture was reacted with heating and refluxing for 4 hours. The organiclayer was washed with purified water and dried with magnesium sulfate.Thereafter, the solvent was distilled off under reduced pressure. Theresidue was purified by silica gel column chromatography to obtaincompound 9 (6.4 g).

Into a 200-mL four-necked flask were introduced the compound 9 (3.8 g;6.2 mmol), the compound 4 (2.3 g; 7.4 mmol), NaOtBu (2.0 g; 21 mmol),and 76 mL of toluene. Nitrogen bubbling was conducted for 30 minutes(solution A).

On the other hand, tri-t-butylphosphine (50 mg) was added to a toluenesolution (6 mL) of a tris(dibenzylideneacetone)dipalladium chloroformcomplex (32 mg), and the mixture was heated to 65° C. (solution B). In anitrogen stream, solution B was added to solution A, and this mixturewas reacted with heating and refluxing for 4 hours. The organic layerwas washed with purified water and dried with magnesium sulfate.Thereafter, the solvent was distilled off under reduced pressure. Theresidue was purified by silica gel column chromatography to obtaincompound II (4.4 g).

Synthesis of Compound III

Into a 100-mL four-necked flask were introduced the compound 9 (0.65 g;1.1 mmol), 4-bromobiphenyl (0.36 g; 1.3 mmol), NaOtBu (0.35 g; 3.6mmol), and 30 mL of toluene. Nitrogen bubbling was conducted for 30minutes (solution A).

On the other hand, tri-t-butylphosphine (8.6 mg) was added to a toluenesolution (5 mL) of a tris(dibenzylideneacetone)dipalladium chloroformcomplex (5.5 mg), and the mixture was heated to 65° C. (solution B). Ina nitrogen stream, solution B was added to solution A, and this mixturewas reacted with heating and refluxing for 4 hours. The organic layerwas washed with purified water and dried with magnesium sulfate.Thereafter, the solvent was distilled off under reduced pressure. Theresidue was purified by silica gel column chromatography and with asublimation purification device to obtain compound III (0.44 g).

Synthesis of Compound X-C

Into a 300-mL four-necked flask were introduced the compound 9 (0.43 g;0.70 mmol), 4-bromoterphenyl (0.26 g; 0.84 mmol), NaOtBu (0.23 g; 2.4mmol), and 10 mL of toluene. Nitrogen bubbling was conducted for 30minutes (solution A).

On the other hand, tri-t-butylphosphine (5.7 mg) was added to a toluenesolution (5 mL) of a tris(dibenzylideneacetone)dipalladium chloroformcomplex (3.6 mg), and the mixture was heated to 65° C. (solution B). Ina nitrogen stream, solution B was added to solution A, and this mixturewas reacted with heating and refluxing for 4 hours. The organic layerwas washed with purified water and dried with magnesium sulfate.Thereafter, the solvent was distilled off under reduced pressure. Theresidue was purified by silica gel column chromatography and with asublimation purification device to obtain compound X-C (0.13 g).

Example 2

An organic electroluminescent element of the structure shown in FIG. 1was produced in the following manner. A glass substrate 1 having a sizeof 25 mm×37.5 mm (thickness, 0.7 mm) was cleaned by subjecting thesubstrate to ultrasonic cleaning with an aqueous surfactant solution,rinsing with ultrapure water, ultrasonic cleaning with ultrapure water,and rinsing with ultrapure water in this order, subsequently dried bynitrogen blowing, and finally subjected to ultraviolet/ozone cleaning.

A transparent conductive film of indium-tin oxide (ITO) was deposited ina thickness of 70 nm on the glass substrate 1 (the film was deposited bysputtering; sheet resistivity, 15Ω), and this coated substrate wasprocessed by an ordinary technique of photolithography to pattern theconductive film into stripes having a width of 2 mm. Thus, an anode 2was formed.

The substrate 1 on which the anode 2 had been formed was cleaned bysubjecting the substrate to ultrasonic cleaning with an aqueoussurfactant solution, rinsing with ultrapure water, ultrasonic cleaningwith ultrapure water, and rinsing with ultrapure water in this order,subsequently dried by nitrogen blowing, and finally subjected toultraviolet/ozone cleaning.

The composition used in Example 1 was used as a polymeric material forconstituting a hole injection layer. This composition was applied on theanode 2 by spin coating in the air under the conditions of a spinnerrotation speed of 1,500 rpm and a spinner rotation period of 30 seconds.The coating film was heated at 230° C. for 1 hour to thereby crosslinkthe high-molecular compound P-1 and dry the coating film. Thus, an eventhin film having a thickness of 30 nm (hole injection layer 3) wasformed.

Subsequently, a composition for hole transport layer formation whichincluded a high-molecular compound P-2 having a structure represented bythe following formula (weight-average molecular weight (MwB), 66,000;dispersity ratio, 1.56) as a polymeric material for constituting a holetransport layer and cyclohexylbenzene as a solvent was prepared. Theconcentration of the high-molecular compound P-2 in the composition was1.1% by mass.

This composition was applied on the hole injection layer 3 by spincoating in nitrogen under the conditions of a spinner rotation speed of1,500 rpm and a spinner rotation period of 120 seconds. The coating filmwas heated at 230° C. for 1 hour in nitrogen to thereby crosslink thehigh-molecular compound P-2 and dry the coating film. Thus, an even thinfilm having a thickness of 14 nm (hole transport layer 4) was formed.

Next, a composition for luminescent-layer formation which includedcompound C3 represented by the following formula and the compound IIobtained in Synthesis Example as charge-transporting compounds,phosphorescent metal complex D2, and cyclohexylbenzene as a solvent wasprepared. The concentrations of the compound C3, the compound II, andthe phosphorescent metal complex D2 in the composition were 1.25% bymass, 3.75% by mass, and 0.7% by mass, respectively.

This composition was applied on the hole transport layer 4 by spincoating in nitrogen under the conditions of a spinner rotation speed of1,700 rpm and a spinner rotation period of 120 seconds. The coating filmwas dried at 130° C. for 10 minutes in nitrogen to thereby dry thecoating film. Thus, an even thin film having a thickness of 63 nm(luminescent layer 5) was formed.

Here, the substrate on which the layers including the luminescent layer5 had been formed was transferred into a vacuum deposition apparatus,and the apparatus was evacuated to a degree of vacuum within theapparatus of at least 0.9×10⁻⁶ Torr. Thereafter, a layer of the compoundC2 used in Example 1 was formed on the luminescent layer 5 by vacuumdeposition to obtain a hole blocking layer 6. The rate of deposition wasregulated so as to be in the range of 0.8-1.0 Å/sec, and the layer wasdeposited in a thickness of 10 nm. The degree of vacuum during thedeposition was 0.9×10⁻⁶ Pa.

Subsequently, (ET-1) used in Example 1 was heated and vapor-deposited onthe hole blocking layer 6 to form an electron transport layer 7. Thedegree of vacuum during the deposition was regulated to 0.8×10⁻⁶ Torr,and the rate of deposition was regulated so as to be in the range of0.8-1.0 Å/sec. The layer was deposited in a thickness of 20 nm.

Here, the element in which the layers including the vapor-depositedelectron transport layer 7 had been formed was temporarily taken out anddisposed in another vacuum deposition apparatus. A shadow mask in theform of stripes with a width of 2 mm was brought, as a mask for cathodedeposition, into close contact with the element so that these stripeswere perpendicular to the ITO stripes of the anode 2, and the apparatuswas evacuated to a degree of vacuum within the apparatus of at least2.1×10⁻⁴ Pa.

First, lithium fluoride (LiF) was deposited as an electron injectionlayer 8 in a thickness of 0.5 nm on the electron transport layer 7 at adeposition rate of 0.08-0.14 Å/sec using a molybdenum boat. The degreeof vacuum during the deposition was 2.7×10⁻⁴ Pa.

Next, aluminum was likewise heated using a molybdenum boat, and analuminum layer having a thickness of 80 nm was formed as a cathode 9while regulating the rate of deposition so as to be in the range of1.0-5.1 Å/sec. The degree of vacuum during the deposition was 5.1×10⁻⁴Pa. During the deposition of these two layers, the temperature of thesubstrate was kept at room temperature.

Subsequently, the same sealing as in Example 1 was conducted in order toprevent the element from being deteriorated by the action of atmosphericmoisture, etc. during storage.

Thus, an organic electroluminescent element having a luminescent areawith a size of 2 mm×2 mm was obtained. This element had the followingluminescent characteristics. The operating voltage thereof at 10 mA/cm²was 7.18 V. The time period required for the luminance thereof todecrease to 95% of the initial luminance was 40 hours, and the increasein operating voltage which was observed when the luminance of theelement had decreased to 95% of the initial luminance was 0.05 V.

Example 3

The same procedure as in Example 2 was conducted, except that compoundIII was used in place of the compound II.

This element had the following luminescent characteristics. Theoperating voltage thereof at 10 mA/cm² was 7.12 V. The time periodrequired for the luminance thereof to decrease to 95% of the initialluminance was 40 hours, and the increase in operating voltage which wasobserved when the luminance of the element had decreased to 95% of theinitial luminance was 0.06 V.

COMPARATIVE EXAMPLE 3

The same procedure as in Example 2 was conducted, except that thecompound X-A was used in place of the compound II. This element had thefollowing luminescent characteristics. The operating voltage thereof at10 mA/cm² was 8.63 V. The time period required for the luminance thereofto decrease to 95% of the initial luminance was 20 hours, and theincrease in operating voltage which was observed when the luminance ofthe element had decreased to 95% of the initial luminance was 0.19 V.

COMPARATIVE EXAMPLE 4

The same procedure as in Example 2 was conducted, except that thecompound X-C was used in place of the compound II. The compound X-Ccrystallized after dissolved, and production of an element wasimpossible.

The results obtained above are summarized in Table 2.

TABLE 2 Increase Time period to in operating voltage decrease to 95% ofOperating in constant-current initial luminance voltage driving Example2 40 h 7.18 V +0.05 V Example 3 40 h 7.12 V +0.06 V Comparative 20 h8.63 V +0.19 V Example 3 Comparative production of element wasimpossible because of Example 4 insufficient solubility

The results showed that the organic electroluminescent elementsemploying the charge transport materials of the invention had a lowoperating voltage and a long working life and showed only a slightincrease in voltage during driving.

INDUSTRIAL APPLICABILITY

The charge transport material of the invention is suitable for use invarious fields in which organic EL elements are used, for example, inthe fields of flat panel displays (e.g., displays for OA computers andwall-mounted TV receivers), light sources taking advantage of thefeature of a surface light emitter (e.g., the light source of a copierand the backlight of a liquid-crystal display or instrument), displaypanels, marker lights, and the like.

Furthermore, since the charge transport material of the inventionessentially has excellent stability to oxidation and reduction, thematerial is useful not only in organic electroluminescent elements butalso in general organic devices including electrophotographicphotoreceptors and organic solar cells.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof. This application is basedon a Japanese patent application filed on Aug. 27, 2009 (Application No.2009-196782), the entire contents thereof being incorporated herein byreference.

DESCRIPTION OF THE REFERENCE NUMERALS

-   1 Substrate-   2 Anode-   3 Hole injection layer-   4 Hole transport layer-   5 Luminescent layer-   6 Hole blocking layer-   7 Electron transport layer-   8 Electron injection layer-   9 Cathode

1. A monoamine compound represented by the following general formula(1):

[wherein R¹ to R³ each independently represent a phenyl group which mayhave a substituent in at least one of o- and m-positions, in which thesubstituent may be bonded to each other to form a cyclic structure, andR¹ to R³ are a group different from each other]. 2-12. (canceled)